APSET
   A project to provide better run-time profiling information for GpH.
   http://www.cee.hw.ac.uk/~gnik/apset/

Buddha
   A declarative debugger for the Haskell 98.
   http://www.cs.mu.oz.au/~bjpop/buddha/

DrIFT
   A Haskell preprocessor for generating instances of classes.
   http://www.dcs.gla.ac.uk/~nww/derivehome.html

Green Card
   A foreign function interface preprocessor, simplifying the task of interfacing Haskell programs to external libraries.
   http://haskell.cs.yale.edu/greencard/

Happy
   A parser generator for Haskell.
   http://haskell.cs.yale.edu/happy/

HaskellDirect
   An (Independent definition language) IDL compiler for Haskell. Can be used to interface foreign language libraries and call COM methods from Haskell.
   http://haskell.cs.yale.edu/hdirect/

The Haskell FFI Binding Modules Generator (HSFFIG)
   A tool that takes a C library include file (.h) and generates Haskell Foreign Functions Interface import declarations for items (functions, structures, etc.) the header defines. [Open source, BSD License]
   http://hsffig.sourceforge.net