diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+1.4.16
+
+- Add [`Control.Foldl.postmapM`]
+
+1.4.15
+
+- Add `Cosieve` and `Costrong` instances
+
 1.4.14
 
 - Add [`Control.Foldl.NonEmpty.nonEmpty`](https://github.com/Gabriella439/foldl/pull/186)
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -136,7 +136,7 @@
 
 ## Development Status
 
-[![Build Status](https://travis-ci.org/Gabriella439/Haskell-Foldl-Library.png)](https://travis-ci.org/Gabriella439/Haskell-Foldl-Library)
+[![Build Status](https://github.com/Gabriella439/foldl/actions/workflows/haskell.yml/badge.svg)](https://github.com/Gabriella439/foldl/actions/workflows/haskell.yml)
 
 The `foldl` library is pretty stable at this point.  I don't expect there to be
 breaking changes to the API from this point forward unless people discover new
diff --git a/foldl.cabal b/foldl.cabal
--- a/foldl.cabal
+++ b/foldl.cabal
@@ -1,5 +1,5 @@
 Name: foldl
-Version: 1.4.15
+Version: 1.4.16
 Cabal-Version: >=1.10
 Build-Type: Simple
 License: BSD3
@@ -25,13 +25,13 @@
     HS-Source-Dirs: src
     Build-Depends:
         base         >= 4.11.0.0 && < 5   ,
-        bytestring   >= 0.9.2.1  && < 0.12,
+        bytestring   >= 0.9.2.1  && < 0.13,
         random       >= 1.2      && < 1.3 ,
-        primitive                   < 0.9 ,
-        text         >= 0.11.2.0 && < 2.1 ,
+        primitive                   < 0.10,
+        text         >= 0.11.2.0 && < 2.2 ,
         transformers >= 0.2.0.0  && < 0.7 ,
         vector       >= 0.7      && < 0.14,
-        containers   >= 0.5.0.0  && < 0.7 ,
+        containers   >= 0.5.0.0  && < 0.8 ,
         unordered-containers        < 0.3 ,
         hashable                    < 1.5 ,
         contravariant               < 1.6 ,
diff --git a/src/Control/Foldl.hs b/src/Control/Foldl.hs
--- a/src/Control/Foldl.hs
+++ b/src/Control/Foldl.hs
@@ -123,6 +123,7 @@
     , _Fold1
     , premap
     , premapM
+    , postmapM
     , prefilter
     , prefilterM
     , predropWhile
@@ -300,7 +301,7 @@
     mempty = pure mempty
     {-# INLINE mempty #-}
 
-    mappend = liftA2 mappend
+    mappend = (<>)
     {-# INLINE mappend #-}
 
 instance Num b => Num (Fold a b) where
@@ -434,7 +435,7 @@
     mempty = pure mempty
     {-# INLINE mempty #-}
 
-    mappend = liftA2 mappend
+    mappend = (<>)
     {-# INLINE mappend #-}
 
 instance (Monad m, Num b) => Num (FoldM m a b) where
@@ -1226,6 +1227,19 @@
   where
     step' x a = f a >>= step x
 {-# INLINABLE premapM #-}
+
+{-| @(postmapM f folder)@ returns a new 'FoldM' where f is applied to the final value.
+
+> postmapM return = id
+>
+> postmapM (f >=> g) = postmapM g . postmapM f
+
+> postmapM k (pure r) = k r
+-}
+postmapM :: Monad m => (a -> m r) -> FoldM m x a -> FoldM m x r
+postmapM f (FoldM step begin done) = FoldM step begin done'
+  where done' x = done x >>= f
+{-# INLINABLE postmapM #-}
 
 {-| @(prefilter f folder)@ returns a new 'Fold' where the folder's input is used
   only when the input satisfies a predicate f
diff --git a/src/Control/Foldl/NonEmpty.hs b/src/Control/Foldl/NonEmpty.hs
--- a/src/Control/Foldl/NonEmpty.hs
+++ b/src/Control/Foldl/NonEmpty.hs
@@ -54,7 +54,7 @@
     mempty = pure mempty
     {-# INLINE mempty #-}
 
-    mappend = liftA2 mappend
+    mappend = (<>)
     {-# INLINE mappend #-}
 
 instance Num b => Num (Fold1 a b) where
diff --git a/src/Control/Scanl.hs b/src/Control/Scanl.hs
--- a/src/Control/Scanl.hs
+++ b/src/Control/Scanl.hs
@@ -149,7 +149,7 @@
     mempty = pure mempty
     {-# INLINE mempty #-}
 
-    mappend = liftA2 mappend
+    mappend = (<>)
     {-# INLINE mappend #-}
 
 instance Num b => Num (Scan a b) where
@@ -299,7 +299,7 @@
     mempty = pure mempty
     {-# INLINE mempty #-}
 
-    mappend = liftA2 mappend
+    mappend = (<>)
     {-# INLINE mappend #-}
 
 instance (Monad m, Num b) => Num (ScanM m a b) where