diff --git a/AddOne.hs b/AddOne.hs
new file mode 100644
--- /dev/null
+++ b/AddOne.hs
@@ -0,0 +1,15 @@
+module Main where
+
+import Data.Default ( def )
+import System.Environment ( getArgs )
+import System.Daemon
+
+addOne :: Int -> IO Int
+addOne n = return (n + 1)
+
+main :: IO ()
+main = do
+    startDaemon "addOne" def addOne
+    [n] <- getArgs
+    res <- runClient "localhost" 5000 ((read n) :: Int)
+    print (res :: Maybe Int)
diff --git a/Control/Pipe/C3.hs b/Control/Pipe/C3.hs
new file mode 100644
--- /dev/null
+++ b/Control/Pipe/C3.hs
@@ -0,0 +1,40 @@
+module Control.Pipe.C3 (
+        -- * Pipes
+        commandSender, commandReceiver
+    ) where
+
+import Control.Monad ( forever )
+import Control.Monad.Trans.Class ( lift )
+import Control.Pipe ( runPipe, await, yield, (<+<) )
+import Control.Pipe.Serialize ( serializer, deserializer )
+import Control.Pipe.Socket ( Handler )
+import Data.Serialize ( Serialize )
+
+-- | Send a single command over the outgoing pipe and wait for a
+-- response.  If the incoming pipe is closed before a response
+-- arrives, returns @Nothing@.
+commandSender :: (Serialize a, Serialize b) => a -> Handler (Maybe b)
+commandSender command reader writer = do
+    runPipe (writer <+< serializer <+< sendCommand)
+    runPipe (receiveResponse
+             <+< (deserializer >> return Nothing)
+             <+< (reader >> return Nothing))
+  where
+    sendCommand = do
+        yield command
+
+    receiveResponse = do
+        res <- await
+        return (Just res)
+
+-- | Wait for commands on the incoming pipe, handle them, and send the
+-- reponses over the outgoing pipe.
+commandReceiver :: (Serialize a, Serialize b) => (a -> IO b) -> Handler ()
+commandReceiver executeCommand reader writer = do
+    runPipe (writer <+< serializer
+             <+< commandExecuter
+             <+< deserializer <+< reader)
+  where
+    commandExecuter = forever $ do
+        comm <- await
+        yield =<< lift (executeCommand comm)
diff --git a/Control/Pipe/Serialize.hs b/Control/Pipe/Serialize.hs
new file mode 100644
--- /dev/null
+++ b/Control/Pipe/Serialize.hs
@@ -0,0 +1,48 @@
+-- | This module provides the 'deserializer' and 'serializer' pipes to
+-- convert 'B.ByteString's off of pipes into typed values.
+--
+-- In order to use it, the types of the values need to have
+-- 'Serialize' instances.  These can be derived automatically using
+-- "Ghc.Generics":
+--
+-- > {-# LANGUAGE DeriveGeneric #-}
+-- >
+-- > data Foo = Bar String | Baz Int
+-- >            deriving ( Generic )
+-- >
+-- > instance Serialize Foo
+--
+-- Note that in the above example: we use the @DeriveGeneric@
+-- extension, derive a @Generic@ instance for our data-type, and write
+-- an /empty/ @Serialize@ instance.
+--
+module Control.Pipe.Serialize (
+        -- * Pipes
+        serializer, deserializer
+    ) where
+
+import Data.ByteString.Char8 ( ByteString )
+import Data.Serialize ( Serialize, get, encode
+                      , Result(..), runGetPartial )
+import Control.Pipe ( Pipe, await, yield )
+import Control.Monad ( forever )
+
+-- | De-serialize data from strict 'ByteString's.  Uses @cereal@'s
+-- incremental 'Data.Serialize.Get' parser.
+deserializer :: (Serialize a, Monad m) => Pipe ByteString a m ()
+deserializer = loop Nothing Nothing
+  where
+    loop mk mbin = do
+        bin <- maybe await return mbin
+        case (maybe (runGetPartial get) id mk) bin of
+          Fail reason -> fail reason
+          Partial k   -> loop (Just k) Nothing
+          Done c bin' -> do
+              yield c
+              loop Nothing (Just bin')
+
+-- | Serialize data into strict 'ByteString's.
+serializer :: (Serialize a, Monad m) => Pipe a ByteString m ()
+serializer = forever $ do
+    x <- await
+    yield (encode x)
diff --git a/Control/Pipe/Socket.hs b/Control/Pipe/Socket.hs
new file mode 100644
--- /dev/null
+++ b/Control/Pipe/Socket.hs
@@ -0,0 +1,79 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+
+-- Thank you:
+--   <a href="https://github.com/pcapriotti/pipes-network">pipes-network</a>
+
+module Control.Pipe.Socket (
+        -- * Socket pipes
+        socketReader, socketWriter,
+
+        -- * Socket server/client
+        Handler, runSocketServer, runSocketClient
+    ) where
+
+import Control.Concurrent ( forkIO )
+import qualified Control.Exception as CE
+import Control.Monad ( forever, unless )
+import Control.Monad.IO.Class ( MonadIO(..) )
+import Control.Monad.Trans.Class ( lift )
+import Control.Pipe ( Consumer, Producer, await, yield )
+import Data.ByteString.Char8 ( ByteString )
+import qualified Data.ByteString.Char8 as B
+import Network.Socket ( Socket )
+import qualified Network.Socket as NS
+import Network.Socket.ByteString ( sendAll, recv )
+
+-- | Stream data from the socket.
+socketReader :: (MonadIO m) => Socket -> Producer ByteString m ()
+socketReader socket = do
+    bin <- lift . liftIO $ recv socket 4096
+    unless (B.null bin) $ do
+        yield bin
+        socketReader socket
+
+-- | Stream data to the socket.
+socketWriter :: (MonadIO m) => Socket -> Consumer ByteString m ()
+socketWriter socket = forever $ do
+    bin <- await
+    lift . liftIO $ sendAll socket bin
+
+-- | A simple handler: takes an incoming stream of 'ByteString's, an
+-- stream of 'ByteString's, and ties them together somehow.
+-- Conceptually, the simplest handler would be @identity@:
+--
+-- > import Control.Monad
+-- > import Control.Pipe
+-- > import Data.ByteString.Char8
+-- >
+-- > handler reader writer = do
+-- >     let identity = forever $ do
+-- >         x <- await
+-- >         yield x
+-- >     runPipe (writer <+< identity <+< reader)
+--
+-- See the @pipes@ tutorial for more examples of writing pipes.
+--
+-- Since 'ByteString's are fairly boring by themseleves, have a look
+-- at "Control.Pipe.Serialize" which lets you deserialize/serialize
+-- pipes of 'ByteString's easily.
+type Handler r = Producer ByteString IO ()
+              -> Consumer ByteString IO ()
+              -> IO r
+
+-- | Listen for connections on the given socket, and run 'Handler' on
+-- each received connection.  The socket should previously have been
+-- bound to a port or to a file.  Each handler is run in its own
+-- thread.  Even in case of an error, the handlers' sockets are
+-- closed.
+runSocketServer :: (MonadIO m) => Socket -> Handler () -> m ()
+runSocketServer lsocket handler = liftIO $ forever $ do
+    (socket, _addr) <- NS.accept lsocket
+    _ <- forkIO $ CE.finally
+                      (handler (socketReader socket) (socketWriter socket))
+                      (NS.sClose socket)
+    return ()
+
+-- | Run 'Handler' on the given socket.
+runSocketClient :: (MonadIO m) => Socket -> Handler r -> m r
+runSocketClient socket handler = liftIO $ do
+    handler (socketReader socket) (socketWriter socket)
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,675 @@
+              GNU GENERAL PUBLIC LICENSE
+                Version 3, 29 June 2007
+
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+
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+
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+
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+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
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+    Copyright (C) <year>  <name of author>
+
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+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
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+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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+
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+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
+
diff --git a/Makefile b/Makefile
new file mode 100644
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,25 @@
+.PHONY: all build dist install test clean doc
+
+all: build test
+
+build: dist/setup-config
+	grep -E "$    " Memo.md | sed 's/$     //' > Memo.hs
+	cabal build
+
+dist: test
+	cabal sdist
+
+install: build
+	cabal install
+
+test: build
+	cabal test
+
+clean:
+	cabal clean
+
+dist/setup-config: daemons.cabal
+	cabal configure --enable-tests
+
+doc: build
+	cabal haddock
diff --git a/Memo.hs b/Memo.hs
new file mode 100644
--- /dev/null
+++ b/Memo.hs
@@ -0,0 +1,59 @@
+{-# LANGUAGE DeriveGeneric, OverloadedStrings #-}
+
+module Main where
+
+import Control.Concurrent.MVar ( MVar, newMVar, modifyMVar )
+import Data.ByteString.Char8 ( ByteString )
+import Data.Default ( def )
+import Data.Serialize ( Serialize )
+import Data.String ( fromString )
+import qualified Data.Map as M
+import GHC.Generics
+import System.Environment ( getArgs )
+import System.Daemon
+
+data Command = Put ByteString ByteString
+             | Get ByteString
+               deriving ( Generic, Show )
+
+instance Serialize Command
+
+data Response = Failed String
+              | Value ByteString
+                deriving ( Generic, Show )
+
+instance Serialize Response
+
+type Book = M.Map ByteString ByteString
+
+handleCommand :: MVar Book -> Command -> IO Response
+handleCommand bookVar comm = modifyMVar bookVar $ \book -> return $
+    case comm of
+      Get key -> ( book
+                 , maybe (Failed "not found") Value (M.lookup key book) )
+      Put key value -> ( M.insert key value book
+                       , Value "ok" )
+
+main :: IO ()
+main = do
+    bookVar <- newMVar M.empty
+    let options = def { daemonPort = 7856 }
+    startDaemon "memo" options (handleCommand bookVar)
+    args <- getArgs
+    let args' = map fromString args
+    res <- case args' of
+      ["get", key]        -> runClient "localhost"  7856 (Get key)
+      ["put", key, value] -> runClient "localhost"  7856 (Put key value)
+      _                   -> error "invalid command"
+    print (res :: Maybe Response)
+
+{-
+% dist/build/memo/memo get apples
+Just (Failed "not found")
+
+% dist/build/memo/memo put apples 23
+Just (Value "ok")
+
+% dist/build/memo/memo get apples
+Just (Value "23")
+-}
diff --git a/NEWS.md b/NEWS.md
new file mode 100644
--- /dev/null
+++ b/NEWS.md
diff --git a/PMTQ.hs b/PMTQ.hs
new file mode 100644
--- /dev/null
+++ b/PMTQ.hs
@@ -0,0 +1,98 @@
+{-# LANGUAGE DeriveGeneric, OverloadedStrings #-}
+
+module Main where
+
+import Control.Concurrent.Chan ( Chan, newChan, readChan, writeChan )
+import Control.Concurrent.MVar ( MVar, newMVar, modifyMVar )
+import Control.Monad ( forever )
+import Control.Monad.Trans.Class ( lift )
+import Control.Pipe ( runPipe, (<+<), await, yield )
+import Control.Pipe.Serialize ( serializer, deserializer )
+import Control.Pipe.Socket ( Handler )
+import Data.ByteString.Char8 ( ByteString )
+import qualified Data.ByteString.Char8 as B
+import Data.Char ( toLower )
+import Data.Default ( def )
+import Data.Serialize ( Serialize )
+import Data.String ( fromString )
+import qualified Data.Map as M
+import GHC.Generics
+import Network.Socket ( withSocketsDo )
+import System.Environment ( getArgs )
+import System.Daemon
+import System.IO ( hPutStrLn, stderr )
+
+data Command = Push ByteString ByteString
+             | Pop ByteString
+             | Consume ByteString
+               deriving ( Generic, Show )
+
+instance Serialize Command
+
+data Response = Value ByteString
+                deriving ( Generic, Show )
+
+instance Serialize Response
+
+type Registry = M.Map ByteString (Chan ByteString)
+
+handleCommands :: MVar Registry -> Handler ()
+handleCommands registryVar reader writer = do
+    runPipe (writer <+< serializer
+             <+< commandExecuter
+             <+< deserializer <+< reader)
+  where
+    commandExecuter = forever $ do
+        comm <- await
+        case comm of
+          Pop topic -> do
+              ch <- lift $ getCreateChan topic
+              transferToPipeFromChan ch
+          Consume topic -> do
+              ch <- lift $ getCreateChan topic
+              forever $ transferToPipeFromChan ch
+          Push topic val -> do
+              ch <- lift $ getCreateChan topic
+              lift $ writeChan ch val
+              yield (Value "ok")
+
+    -- Transfer a value from the given channel to the pipe.
+    transferToPipeFromChan ch = do
+        val <- lift $ readChan ch
+        yield (Value val)
+
+    -- Get the channel for the given topic, and create it if it does
+    -- not already exist.
+    getCreateChan topic = modifyMVar registryVar $ \registry -> do
+        case M.lookup topic registry of
+          Nothing -> do
+              ch <- newChan
+              return (M.insert topic ch registry, ch)
+          Just ch -> do
+              return (registry, ch)
+
+main :: IO ()
+main = withSocketsDo $ do
+    registryVar <- newMVar M.empty
+    let options = def { daemonPort = 7857 }
+    startDaemonWithHandler "pmtq" options (handleCommands registryVar)
+    args <- getArgs
+    let args' = map (fromString . map toLower) args
+    case args' of
+      ["pop", key] -> do
+          res <- runClient "localhost" 7857 (Pop key)
+          printResult res
+      ["push", key, value] -> do
+          res <- runClient "localhost" 7857 (Push key value)
+          printResult res
+      ["consume", key] -> do
+          runClientWithHandler "localhost" 7857 $ \reader writer -> do
+              runPipe (writer <+< serializer <+< yield (Consume key))
+              runPipe ((forever $ await >>= \res -> lift (printResult (Just res)))
+                       <+< deserializer <+< reader)
+      _ -> do
+          error "invalid command"
+  where
+    printResult :: Maybe Response -> IO ()
+    printResult Nothing            = hPutStrLn stderr "no response"
+    printResult (Just (Value val)) = B.putStrLn val
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,80 @@
+daemons
+=======
+
+> Daemons in Haskell made fun and easy
+
+Example
+-------
+
+Here's
+[AddOne](https://github.com/scvalex/daemons/blob/master/AddOne.hs), a
+simple daemon that waits for a number and responds with the
+incremented number.
+
+    import Data.Default ( def )
+    import System.Environment ( getArgs )
+    import System.Daemon
+
+    addOne :: Int -> IO Int
+    addOne n = return (n + 1)
+
+    main :: IO ()
+    main = do
+        startDaemon "addOne" def addOne
+        [n] <- getArgs
+        res <- runClient "localhost" 5000 ((read n) :: Int)
+        print (res :: Maybe Int)
+
+Running it, we see:
+
+    % addone 22
+    Just 23
+    % addone 41
+    Just 42
+
+The two important functions above are `startDaemon`, which checks if a
+daemon named `addOne` is already running, and starts it if not, and
+`runClient` which connects to the daemon running on `localhost:5000`,
+passes it a number, and waits for the response.
+
+For a less trivial example, see the in-memory key-value store,
+[Memo](https://github.com/scvalex/daemons/blob/master/Memo.md).
+
+For an example that uses the streaming interface of `daemons`, see
+[PMTQ](https://github.com/scvalex/daemons/blob/master/PMTQ.hs) (Poor
+Man's Task Queue).
+
+Installation
+------------
+
+This package is on
+[Hackage](http://hackage.haskell.org/package/daemons).  To install
+it, run:
+
+    cabal update
+    cabal install daemons
+
+Modules
+-------
+
+ - `Control.Pipe.C3` provides simple RPC-like wrappers for pipes.
+
+ - `Control.Pipe.Serialize` provides pipes to serialize and
+   deserialize streams of strict `ByteString`s using
+   [cereal](http://hackage.haskell.org/package/cereal).
+
+ - `Control.Pipe.Socket` provides functions to setup strict
+   `ByteString` pipes around sockets.
+
+ - `System.Daemon` provides a high-level interface to starting
+   daemonized programs that are controlled through sockets.
+
+ - `System.Posix.Daemon` provides a low-level interface to starting,
+   and controlling detached jobs.
+
+See also
+--------
+
+ - `pipes` [The Pipes Tutorial](http://hackage.haskell.org/packages/archive/pipes/latest/doc/html/Control-Pipe-Tutorial.html)
+
+ - `C3` [Wikipedia](https://en.wikipedia.org/wiki/Command,_control,_and_communications#Command.2C_control_and_communications)
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/System/Daemon.hs b/System/Daemon.hs
new file mode 100644
--- /dev/null
+++ b/System/Daemon.hs
@@ -0,0 +1,156 @@
+module System.Daemon (
+        -- * Daemons
+        startDaemon, startDaemonWithHandler,
+
+        -- * Clients,
+        runClient, runClientWithHandler,
+
+        -- * Types
+        DaemonOptions(..), PidFile(..), HostName, Port,
+
+        -- * Helpers
+        bindPort, getSocket
+    ) where
+
+import Control.Concurrent ( threadDelay )
+import qualified Control.Exception as CE
+import Control.Monad ( when )
+import Control.Pipe.C3 ( commandSender, commandReceiver )
+import Control.Pipe.Socket ( Handler, runSocketServer, runSocketClient )
+import Data.Default ( Default(..) )
+import Data.Serialize ( Serialize )
+import Data.String ( IsString(..) )
+import Network.Socket ( Socket, SockAddr(..), Family(..), SocketType(..)
+                      , SocketOption(..), setSocketOption
+                      , socket, sClose, connect, bindSocket, listen
+                      , getAddrInfo, addrAddress
+                      , defaultProtocol, iNADDR_ANY, maxListenQueue )
+import System.Directory ( getHomeDirectory )
+import System.FilePath ( (</>), (<.>) )
+import System.Posix.Daemon ( runDetached, isRunning )
+
+type Port = Int
+type HostName = String
+
+-- | The configuration options of a daemon.  See 'startDaemon' for a
+-- description of each.
+data DaemonOptions = DaemonOptions
+    { daemonPort     :: Port
+    , daemonPidFile  :: PidFile
+    } deriving ( Show )
+
+instance Default DaemonOptions where
+    def = DaemonOptions { daemonPort    = 5000
+                        , daemonPidFile = InHome
+                        }
+
+-- | The location of the daemon's pidfile.
+data PidFile = InHome
+             | PidFile FilePath
+               deriving ( Show )
+
+instance IsString PidFile where
+    fromString = PidFile
+
+-- | Simple wrapper around 'startDaemonWithHandler' which uses a
+-- simple function to respond to commands and doesn't deal with pipes.
+--
+-- The @handler@ is just a function that takes a command and returns a
+-- response.
+startDaemon :: (Serialize a, Serialize b)
+            => String         -- ^ name
+            -> DaemonOptions  -- ^ options
+            -> (a -> IO b)    -- ^ handler
+            -> IO ()
+startDaemon name options executeCommand = do
+    startDaemonWithHandler name options (commandReceiver executeCommand)
+
+-- | Start a daemon running on the given port, using the given handler
+-- to respond to events.  If the daemon is already running, just
+-- return.
+--
+-- The pidfile @PidFile options@ will be created and locked.  This
+-- function checks the pidfile to see if the daemon is already
+-- running.
+--
+-- The daemon will listen for incoming connections on all interfaces
+-- on @daemonPort options@.
+--
+-- The @handler@ is a function that takes the reader and writer
+-- 'ByteString' pipes and does something with them.  See
+-- 'commandReceiver' for an example handler.
+startDaemonWithHandler :: String         -- ^ name
+                       -> DaemonOptions  -- ^ options
+                       -> Handler ()     -- ^ handler
+                       -> IO ()
+startDaemonWithHandler name options handler = do
+    home <- getHomeDirectory
+    let pidfile = case daemonPidFile options of
+                    InHome       -> home </> ("." ++ name) <.> "pid"
+                    PidFile path -> path
+    running <- isRunning pidfile
+    when (not running) $ do
+        runDetached (Just pidfile) def $ do
+            CE.bracket
+                (bindPort (daemonPort options))
+                sClose
+                (\lsocket ->
+                     runSocketServer lsocket handler)
+        threadDelay 1000000
+
+-- | Send a command to the daemon running at the given network address
+-- and wait for a response.
+--
+-- This is a simple wrapper around 'runClientWithHandler' that sends a
+-- single command and waits for a single response.
+--
+-- If the connection is closed before receiving a response, return
+-- 'Nothing'.
+runClient :: (Serialize a, Serialize b)
+          => HostName  -- ^ hostname
+          -> Port      -- ^ port
+          -> a         -- ^ command
+          -> IO (Maybe b)
+runClient hostname port comm =
+    runClientWithHandler hostname port (commandSender comm)
+
+-- | Connect to the given network address and run the handler on the
+-- reader and wrier pipes for the socket.
+--
+-- The @handler@ is a function that takes the reader and writer
+-- 'ByteString' pipes and does something with them.  For an example
+-- handler, see 'commandSender', which sends a command and waits for a
+-- response.
+runClientWithHandler :: HostName   -- ^ hostname
+                     -> Port       -- ^ port
+                     -> Handler a  -- ^ command
+                     -> IO a
+runClientWithHandler hostname port handler = do
+    CE.bracket
+        (getSocket hostname port)
+        sClose
+        (\s -> runSocketClient s handler)
+
+-- | Create a socket and bind it to the given port.
+bindPort :: Port -> IO Socket
+bindPort port = do
+    CE.bracketOnError
+        (socket AF_INET Stream defaultProtocol)
+        sClose
+        (\s -> do
+            setSocketOption s ReuseAddr 1
+            bindSocket s (SockAddrInet (fromIntegral port)
+                                                  iNADDR_ANY)
+            listen s maxListenQueue
+            return s)
+
+-- | Create a socket connected to the given network address.
+getSocket :: HostName -> Port -> IO Socket
+getSocket hostname port = do
+    addrInfos <- getAddrInfo Nothing (Just hostname) (Just $ show port)
+    CE.bracketOnError
+        (socket AF_INET Stream defaultProtocol)
+        sClose
+        (\s -> do
+             connect s (addrAddress $ head addrInfos)
+             return s)
diff --git a/System/Posix/Daemon.hs b/System/Posix/Daemon.hs
new file mode 100644
--- /dev/null
+++ b/System/Posix/Daemon.hs
@@ -0,0 +1,191 @@
+-- | This module provides a simple interface to creating, checking the
+-- status of, and stopping background jobs.
+--
+-- Use 'runDetached' to start a background job.  For instance, here is
+-- a daemon that peridically hits a webserver:
+--
+-- > import Control.Concurrent
+-- > import Control.Monad
+-- > import Data.Default
+-- > import Data.Maybe
+-- > import Network.BSD
+-- > import Network.HTTP
+-- > import Network.URI
+-- > import System.Posix.Daemon
+-- >
+-- > main :: IO ()
+-- > main = runDetached (Just "diydns.pid") def $ forever $ do
+-- >     hostname <- getHostName
+-- >     _ <- simpleHTTP
+-- >              (Request { rqURI     = fromJust (parseURI "http://foo.com/dns")
+-- >                       , rqMethod  = GET
+-- >                       , rqHeaders = []
+-- >                       , rqBody    = hostname })
+-- >     threadDelay (600 * 1000 * 1000)
+--
+-- To check if the above job is running, use 'isRunning' with the same
+-- pidfile:
+--
+-- > isRunning "diydns.pid"
+--
+-- Finally, to stop the above job (maybe because we're rolling a new
+-- version of it), use 'kill':
+--
+-- > kill "diydns.pid"
+--
+-- As a side note, the code above is a script that the author uses as
+-- a sort of homebrew dynamic DNS: the remote address is a CGI script
+-- that records the IP addresses of all incoming requests in separate
+-- files named after the contents of the requests; the addresses are
+-- then viewable with any browser.
+module System.Posix.Daemon (
+        -- * Starting
+        runDetached, Redirection(..),
+
+        -- * Status
+        isRunning,
+
+        -- * Stopping
+        kill, brutalKill
+    ) where
+
+import Prelude hiding ( FilePath )
+
+import Control.Monad ( when )
+import Data.Default ( Default(..) )
+import System.Directory ( doesFileExist )
+import System.FilePath ( FilePath )
+import System.IO ( SeekMode(..), hFlush, stdout )
+import System.Posix.Files ( stdFileMode )
+import System.Posix.IO ( openFd, OpenMode(..), defaultFileFlags, closeFd
+                       , dupTo, stdInput, stdOutput, stdError, getLock
+                       , createFile
+                       , LockRequest (..), setLock, fdWrite, fdRead )
+import System.Posix.Process ( getProcessID, forkProcess, createSession )
+import System.Posix.Signals ( Signal, signalProcess, sigQUIT, sigKILL )
+
+-- | Where should the output (and input) of a daemon be redirected to?
+-- (we can't just leave it to the current terminal, because it may be
+-- closed, and that would kill the daemon).
+--
+-- When in doubt, just use 'def', the default value.
+--
+-- 'DevNull' causes the output to be redirected to @\/dev\/null@.  This
+-- is safe and is what you want in most cases.
+--
+-- If you don't want to lose the output (maybe because you're using it
+-- for logging), use 'ToFile', instead.
+data Redirection = DevNull
+                 | ToFile FilePath
+                   deriving ( Show )
+
+instance Default Redirection where
+    def = DevNull
+
+-- | Run the given action detached from the current terminal; this
+-- creates an entirely new process.  This function returns
+-- immediately.  Uses the double-fork technique to create a well
+-- behaved daemon.  If @pidfile@ is given, check/write it; if we
+-- cannot obtain a lock on the file, another process is already using
+-- it, so fail.  The @redirection@ parameter controls what to do with
+-- the standard channels (@stdin@, @stderr@, and @stdout@).
+--
+-- See: <http://www.enderunix.org/docs/eng/daemon.php>
+--
+-- Note: All unnecessary fds should be close before calling this.
+-- Otherwise, you get an fd leak.
+runDetached :: Maybe FilePath  -- ^ pidfile
+            -> Redirection     -- ^ redirection
+            -> IO ()           -- ^ program
+            -> IO ()
+runDetached maybePidFile redirection program = do
+    -- check if the pidfile exists; fail if it does
+    checkPidFile
+    -- fork first child
+    ignore $ forkProcess $ do
+        -- create a new session and make this process its leader; see
+        -- setsid(2)
+        ignore $ createSession
+        -- fork second child
+        ignore $ forkProcess $ do
+            -- create the pidfile
+            writePidFile
+            -- remap standard fds
+            remapFds
+            -- run the daemon
+            program
+  where
+    ignore act = act >> return ()
+
+    -- Remap the standard channels based on the @redirection@
+    -- parameter.
+    remapFds = do
+        devnull <- openFd "/dev/null" ReadOnly Nothing defaultFileFlags
+        ignore (dupTo devnull stdInput)
+        closeFd devnull
+
+        let file = case redirection of
+                     DevNull         -> "/dev/null"
+                     ToFile filepath -> filepath
+        fd <- openFd file ReadWrite (Just stdFileMode) defaultFileFlags
+        hFlush stdout
+        mapM_ (dupTo fd) [stdOutput, stdError]
+        closeFd fd
+
+    -- Convert the 'FilePath' @pidfile@ to a regular 'String' and run
+    -- the action with it.
+    withPidFile act =
+        case maybePidFile of
+          Nothing      -> return ()
+          Just pidFile -> act pidFile
+
+    -- Check if the pidfile exists; fail if it does, and create it, otherwise
+    checkPidFile = withPidFile $ \pidFile -> do
+        running <- isRunning pidFile
+        when running $ fail "already running"
+
+    writePidFile = withPidFile $ \pidFile -> do
+        fd <- createFile pidFile stdFileMode
+        setLock fd (WriteLock, AbsoluteSeek, 0, 0)
+        pid <- getProcessID
+        ignore $ fdWrite fd (show pid)
+        -- note that we do not close the fd; doing so would release
+        -- the lock
+
+-- | Return 'True' if the given file is locked by a process.  In our
+-- case, returns 'True' when the daemon that created the file is still
+-- alive.
+isRunning :: FilePath -> IO Bool
+isRunning pidFile = do
+    dfe <- doesFileExist pidFile
+    if dfe
+      then do
+          fd <- openFd pidFile ReadWrite Nothing defaultFileFlags
+          -- is there an *incompatible* lock on the pidfile?
+          ml <- getLock fd (WriteLock, AbsoluteSeek, 0, 0)
+          (pid, _) <- fdRead fd 100
+          closeFd fd
+          case ml of
+            Nothing -> do
+                pid' <- getProcessID
+                return (read pid == pid')
+            Just _ -> do
+                return True
+      else do
+          return False
+
+-- | Send 'sigQUIT' to the process recorded in the pidfile.  This
+-- gives the process a chance to close cleanly.
+kill :: FilePath -> IO ()
+kill = signalProcessByFilePath sigQUIT
+
+-- | Send 'sigKILL' to the process recorded in the pidfile.  This
+-- immediately kills the process.
+brutalKill :: FilePath -> IO ()
+brutalKill = signalProcessByFilePath sigKILL
+
+-- | Send a signal to a process whose pid is recorded in a file.
+signalProcessByFilePath :: Signal -> FilePath -> IO ()
+signalProcessByFilePath signal pidFile = do
+    pid <- readFile pidFile
+    signalProcess signal (read pid)
diff --git a/Test/Daemon.hs b/Test/Daemon.hs
new file mode 100644
--- /dev/null
+++ b/Test/Daemon.hs
@@ -0,0 +1,122 @@
+{-# LANGUAGE OverloadedStrings, ScopedTypeVariables #-}
+
+module Main where
+
+import Control.Concurrent
+import Control.Exception
+import Control.Monad
+import Data.Default
+import Data.Monoid
+import System.Directory
+import System.Posix.Daemon
+import System.Posix.Process
+
+import Test.Framework
+import Test.Framework.Providers.HUnit
+import Test.HUnit
+
+main :: IO ()
+main = defaultMainWithOpts
+       [ testCase "firstRun" testFirst
+       , testCase "withPid" testWithPid
+       , testCase "isRunning" testIsRunning
+       , testCase "exclusion" testExclusion
+       , testCase "release" testRelease
+       , testCase "redirection" testRedirection
+       ] mempty
+
+ensureRemoved :: [FilePath] -> IO ()
+ensureRemoved filepaths = forM_ filepaths $ \filepath -> do
+    exists <- doesFileExist filepath
+    when exists $ do
+        removeFile filepath
+
+-- Wait the given number of ms.
+sleep :: Int -> IO ()
+sleep n = threadDelay (n * 1000)
+
+testFirst :: Assertion
+testFirst = flip finally (ensureRemoved ["tmp"]) $ do
+    let txtExp = "42"
+    runDetached Nothing def $ do
+        writeFile "tmp" txtExp
+    sleep 500
+    txt <- readFile "tmp"
+    txt @?= txtExp
+
+testWithPid :: Assertion
+testWithPid = flip finally (ensureRemoved ["pid", "tmp"]) $ do
+    let txtExp = "42"
+    runDetached (Just "pid") def $ do
+        pid <- getProcessID
+        pid' <- readFile "pid"
+        if show pid == pid'
+          then writeFile "tmp" txtExp
+          else writeFile "tmp" "wrong pid recorded"
+    sleep 500
+    txt <- readFile "tmp"
+    txt @?= txtExp
+    pid <- readFile "pid"
+    null pid @?= False
+
+testIsRunning :: Assertion
+testIsRunning = flip finally (ensureRemoved ["pid", "tmp"]) $ do
+    runDetached (Just "pid") def $ do
+        running <- isRunning "pid"
+        writeFile "tmp" (show running)
+        sleep 10000
+    sleep 500
+
+-- FIXME There's some weird behaviour when the process that has locked
+-- the file (or its ancestors, or its descendents) use 'isRunning'.
+--
+-- The semantics of 'fnctl' are "try to aquire the requested lock; if
+-- there is an incompatible lock in place, return it".  Of course,
+-- this means that the process that acquired the lock sees it as
+-- unlocked.
+--
+-- We mitigated the obvious part of the problem (same process) by
+-- checking the pid in the pidfile.  Now, we're left with the case
+-- where an ancestor of the process thinks it can set the lock.
+
+    -- running <- isRunning "pid"
+    -- running @?= True
+    txt <- readFile "tmp"
+    txt @?= "True"
+
+testExclusion :: Assertion
+testExclusion = flip finally (ensureRemoved ["pid", "tmp"]) $ do
+    let txtExp = "ok"
+    runDetached (Just "pid") def $ do
+        sleep 1000
+    sleep 500
+    handle (\(_ :: SomeException) -> writeFile "tmp" txtExp)
+        (runDetached (Just "pid") def $ do
+             writeFile "tmp" "failed")
+    sleep 500
+    txt <- readFile "tmp"
+    txt @?= txtExp
+
+testRelease :: Assertion
+testRelease = flip finally (ensureRemoved ["pid", "tmp"]) $ do
+    let txtExp = "ok"
+    runDetached (Just "pid") def $ do
+        writeFile "tmp" txtExp
+    sleep 500
+    txt <- readFile "tmp"
+    txt @?= txtExp
+    let txtExp' = "ok"
+    runDetached (Just "pid") def $ do
+        writeFile "tmp" txtExp'
+    sleep 500
+    txt' <- readFile "tmp"
+    txt' @?= txtExp'
+
+testRedirection :: Assertion
+testRedirection = flip finally (ensureRemoved ["tmp"]) $ do
+    let txtExp = "ok"
+    runDetached Nothing (ToFile "tmp") $ do
+        putStr "ok"
+    sleep 500
+    txt <- readFile "tmp"
+    txt @?= txtExp
diff --git a/daemons.cabal b/daemons.cabal
new file mode 100644
--- /dev/null
+++ b/daemons.cabal
@@ -0,0 +1,80 @@
+Name:           daemons
+Version:        0.1.0
+Cabal-Version:  >= 1.8
+License:        GPL-3
+License-File:   LICENSE
+Stability:      experimental
+Author:         Alexandru Scvortov <scvalex@gmail.com>
+Maintainer:     scvalex@gmail.com
+Homepage:       https://github.com/scvalex/daemons
+Category:       Text
+Synopsis:       Daemons in Haskell made fun and easy
+Build-Type:     Simple
+Description:
+        "Control.Pipe.C3" provides simple RPC-like wrappers for pipes.
+        .
+        "Control.Pipe.Serialize" provides serialization and
+        incremental deserialization pipes.
+        .
+        "Control.Pipe.Socket" provides functions to setup pipes around
+        sockets.
+        .
+        "System.Daemon" provides a high-level interface to starting
+        daemonized programs that are controlled through sockets.
+        .
+        "System.Posix.Daemon" provides a low-level interface to
+        starting, and controlling detached jobs.
+        .
+        See the @README.md@ file and the homepage for details.
+
+Extra-Source-Files:     Makefile
+
+Data-Files:             README.md, NEWS.md, LICENSE
+
+Source-repository head
+  Type:                 git
+  Location:             git://github.com/scvalex/daemons.git
+
+Library
+  Build-depends:        base >= 4 && < 5, bytestring, cereal,
+                        data-default, directory, filepath, network, pipes,
+                        transformers, unix
+  Ghc-options:          -Wall -threaded
+  Exposed-modules:      Control.Pipe.C3,
+                        Control.Pipe.Serialize,
+                        Control.Pipe.Socket,
+                        System.Daemon,
+                        System.Posix.Daemon
+  Other-modules:
+
+Executable memo
+  Build-depends:        base >= 4 && < 5, bytestring, cereal,
+                        containers, data-default, directory, filepath,
+                        ghc-prim, pipes, transformers, network, unix
+  Main-Is:              Memo.hs
+  Ghc-options:          -Wall
+
+Executable addone
+  Build-depends:        base >= 4 && < 5, bytestring, cereal,
+                        containers, data-default, directory, filepath,
+                        ghc-prim, pipes, transformers, network, unix
+  Main-Is:              AddOne.hs
+  Ghc-options:          -Wall
+
+Executable queue
+  Build-depends:        base >= 4 && < 5, bytestring, cereal,
+                        containers, data-default, directory, filepath,
+                        ghc-prim, pipes, transformers, network, unix
+  Main-Is:              PMTQ.hs
+  Ghc-options:          -Wall
+
+Test-suite daemon
+  Hs-Source-Dirs:       Test, .
+  Main-Is:              Daemon.hs
+  Type:                 exitcode-stdio-1.0
+
+  Build-Depends:        base >= 4 && < 5, data-default, directory,
+                        filepath, unix
+  Ghc-Options:          -Wall
+
+  Build-Depends:        test-framework, test-framework-hunit, HUnit