diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,104 @@
+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0)
+and this project adheres to
+[Compatible Versioning](https://github.com/staltz/comver).
+
+## [Unreleased]
+
+## [0.6] - 2019-04-25
+### Added
+- Schema language: `RGA` type.
+
+## [0.5] - 2019-02-04
+### Added
+- `RON.UUID.liftName` function to create name UUIDs in compile time.
+- `RON.Util.ByteStringL` type.
+- `RON.Error` module with unified pretty errors.
+- Organize `Replicated`, `ReplicatedAsPayload`, and `ReplicatedAsObject` in
+  class hierarchy.
+- Add `ORSet.removeValue` and `removeRef` implementation.
+- Op "patterns" and patterns.
+
+### Removed
+- Type alias `ObjectId` since objects are identified by UUID.
+
+### Changed
+- Extracted `ron-storage` package.
+- Extracted `ron-schema` package.
+- Extracted `ron-rdt` package.
+- Switched from `Either String a` to `MonadError String m => m a` in failable
+  procedures.
+- `ORSet.addRef` now adds item's frame, too.
+- `ORSet.addNewRef` now returns the reference to the freshly created object.
+- Change `StateFrame` key to UUID since objects are identified by UUID.
+- Renamed `RawOp` to `ClosedOp` according to the fresh spec.
+
+### Fixed
+- Error handling in Boole decoder.
+
+## [0.4] - 2019-01-09
+### Added
+- Schema `enum` declaration.
+- `docIdFromUuid`.
+- `OnDocumentChanged` is called each time when any document is changed.
+
+### Changed
+- Made GHC 8.6 default.
+
+### Removed
+- Schema embedded DSL helpers: `atomInteger`, `atomString`, `boole`, `char`,
+  `field`, `option`, `orSet`, `rgaString`, `structLww`, `versionVector`.
+
+### Fixed
+- `RGA.edit` bug with re-adding deleted items (#39).
+
+## [0.3] - 2018-12-05
+### Added
+- Encode/decode EpochTime.
+- EDN-based schema DSL.
+
+### Removed
+- `RON.Storage.createVersion` from public API.
+- `NFData` instances.
+
+## [0.2] - 2018-11-20
+### Added
+- Schema boole type.
+- RON.Storage and submodules are moved from ff project.
+- RON.Schema is now re-exported via RON.Schema.TH.
+
+### Changed
+- Renamed UUID field "schema" to "version", according to changes in the
+  specification.
+- RGA: sequential UUIDs on initialization.
+- Optimized `Base64.isLetter`.
+- Extend `UUID.mkName` to accept any monad.
+- Renamed `MonadStorage` methods `list...` -> `get...`
+- Renamed `RON.Storage.saveDocument` -> `createDocument`
+
+### Removed
+- `RON.Storage.uuidToFileName` as it has no sense as an abstraction
+- `RON.Storage.IO.runStorageT` with `StorageT`
+
+## [0.1] - 2018-11-08
+### Added
+- Package `ron`
+  - RON-text format
+  - RON-binary format
+  - RON-RDT:
+    - LWW
+    - RGA
+    - OR-Set
+    - VersionVector
+  - RON-Schema
+  - RON-Schema TemplateHaskell code generator
+
+[Unreleased]: https://github.com/ff-notes/ff/compare/ron-schema-0.6...HEAD
+[0.6]: https://github.com/ff-notes/ff/compare/v0.5...ron-schema-0.6
+[0.5]: https://github.com/ff-notes/ff/compare/v0.4...v0.5
+[0.4]: https://github.com/ff-notes/ff/compare/v0.3...v0.4
+[0.3]: https://github.com/ff-notes/ff/compare/v0.2...v0.3
+[0.2]: https://github.com/ff-notes/ff/compare/v0.1...v0.2
+[0.1]: https://github.com/ff-notes/ff/tree/v0.1
diff --git a/lib/RON/Schema/EDN.hs b/lib/RON/Schema/EDN.hs
--- a/lib/RON/Schema/EDN.hs
+++ b/lib/RON/Schema/EDN.hs
@@ -47,6 +47,7 @@
     , ("VersionVector", Type0 $ TObject TVersionVector)
     , ("Option",        Type1 $ TComposite . TOption)
     , ("ORSet",         Type1 $ TObject . TORSet)
+    , ("RGA",           Type1 $ TObject . TRga)
     ]
   where
     char = opaqueAtoms "Char" OpaqueAnnotations{oaHaskellType = Just "Char"}
diff --git a/prelude/Prelude.hs b/prelude/Prelude.hs
--- a/prelude/Prelude.hs
+++ b/prelude/Prelude.hs
@@ -5,13 +5,18 @@
     module X,
     fmapL,
     foldr1,
+    headMay,
     identity,
     lastDef,
     maximumDef,
     maxOn,
     minOn,
+    note,
+    replicateM2,
+    replicateM3,
     show,
     whenJust,
+    (!!),
     (?:),
 ) where
 
@@ -40,10 +45,11 @@
 import           Data.Int as X (Int, Int16, Int32, Int64, Int8)
 import           Data.IORef as X (IORef, atomicModifyIORef', newIORef,
                                   readIORef, writeIORef)
-import           Data.List as X (filter, genericLength, intercalate, isPrefixOf,
-                                 isSuffixOf, lookup, map, partition, repeat,
-                                 replicate, sortBy, sortOn, span, splitAt, take,
-                                 takeWhile, unlines, unwords, zip, (++))
+import           Data.List as X (drop, filter, genericLength, intercalate,
+                                 isPrefixOf, isSuffixOf, lookup, map, partition,
+                                 repeat, replicate, sortBy, sortOn, span,
+                                 splitAt, take, takeWhile, unlines, unwords,
+                                 zip, (++))
 import           Data.List.NonEmpty as X (NonEmpty ((:|)), nonEmpty)
 import           Data.Maybe as X (Maybe (Just, Nothing), catMaybes, fromMaybe,
                                   listToMaybe, maybe, maybeToList)
@@ -131,6 +137,11 @@
 foldr1 :: (a -> a -> a) -> NonEmpty a -> a
 foldr1 = Data.Foldable.foldr1
 
+headMay :: [a] -> Maybe a
+headMay = \case
+    []  -> Nothing
+    a:_ -> Just a
+
 identity :: a -> a
 identity x = x
 
@@ -151,11 +162,25 @@
 minOn :: Ord b => (a -> b) -> a -> a -> a
 minOn f x y = if f x < f y then x else y
 
+note :: e -> Maybe a -> Either e a
+note e = maybe (Left e) Right
+
+replicateM2 :: Applicative m => m a -> m (a, a)
+replicateM2 ma = (,) <$> ma <*> ma
+
+replicateM3 :: Applicative m => m a -> m (a, a, a)
+replicateM3 ma = (,,) <$> ma <*> ma <*> ma
+
 show :: (Show a, IsString s) => a -> s
 show = fromString . Text.Show.show
 
 whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
 whenJust m f = maybe (pure ()) f m
+
+(!!) :: [a] -> Int -> Maybe a
+xs !! i
+    | i < 0     = Nothing
+    | otherwise = headMay $ drop i xs
 
 -- | An infix form of 'fromMaybe' with arguments flipped.
 (?:) :: Maybe a -> a -> a
diff --git a/ron-schema.cabal b/ron-schema.cabal
--- a/ron-schema.cabal
+++ b/ron-schema.cabal
@@ -1,7 +1,7 @@
 cabal-version:  2.2
 
 name:           ron-schema
-version:        0.5
+version:        0.6
 
 bug-reports:    https://github.com/ff-notes/ron/issues
 category:       Distributed Systems, Protocol, Database
@@ -19,7 +19,7 @@
     .
     > import RON.Data
     > import RON.Schema.TH
-    > import RON.Storage.IO as Storage
+    > import RON.Storage.FS as Storage
     >
     > [mkReplicated|
     >     (struct_lww Note
@@ -40,6 +40,9 @@
     >         createDocument obj
 
 build-type:     Simple
+
+extra-source-files:
+    CHANGELOG.md
 
 common language
     build-depends: base >= 4.10 && < 4.13, integer-gmp