Dragen is a Haskell library which can be used to derive test data generators for QuickCheck in Haskell, and hence saves the programmer from the tedious task of writing test data generators manually. It uses probabilistic analysis to derive optimal random generators. Dragen is open source.
Valid Hole Fits is an extension to typed-holes that has been adopted by GHC. It uses type information to automatically suggest and order fits for typed-holes, allowing the programmer to utilize the compiler as an interactive helper while writing code. The extension is open source, and is bundled with GHC (from verison 8.6.1 and onwards).