Libraries

A Compiler Toolkit in Haskell
A set of modules for creating compilers in Haskell. [Open Source, GPL]
http://www.cse.unsw.edu.au/~chak/haskell/ctk/

FranTk
A high level library for building GUIs in Haskell. It provides good support for developing complex dynamic systems, and is built on top of Tcl/Tk. [Open Source, BSD-like]
http://haskell.cs.yale.edu/FranTk/

Fudgets
Graphical User Interface toolkit for Haskell and X Window system. [Free non-commercial use]
http://www.md.chalmers.se/Cs/Research/Functional/Fudgets/

Gtk+Haskell
Bindings for GTK+ for Haskell.
http://www.cse.unsw.edu.au/~chak/haskell/gtk/

Gtk2Hs
A GUI library for Haskell based on Gtk+. [Open source, LGPL]
http://haskell.org/gtk2hs/

Haggis
Multi-threaded, concurrent user interface framework for Haskell, X Window.
http://www.dcs.gla.ac.uk/fp/software/haggis/

HaSQL Project
An ODBC interface to Haskell implemented using Green Card.
http://members.tripod.com/~sproot/hasql.htm

HGL Graphics Library
A portable graphics library for both X11 and Win32. [Open Source, BSD-like]
http://haskell.org/graphics/

HOpenGL
An OpenGL/GLUT binding for Haskell. [Open Source, LGPL]
http://haskell.org/HOpenGL/

Java VM Bridge
A bridge to the Java virtual machine via JNI for Haskell. [Open Source, LGPL]
http://sourceforge.net/projects/jvm-bridge/

MySQL-HS
An interface to the database MySQL for the programming language Haskell. [Open Source, LGPL]
http://www.volker-wysk.de/mysql-hs/

QtHaskell
Haskell bindings for the Qt Widget Library from Trolltech AS.
http://qthaskell.sourceforge.net/

Regular expressions in Haskell
Native Haskell implementation of polymorphic regular expressions. The regexps contains most of the features found in Perl.
http://www.dcs.gla.ac.uk/~meurig/regexp/

TclHaskell
Useful for building graphical user interfaces through the Tcl/Tk. [Open Source, BSD-like]
http://www.dcs.gla.ac.uk/~meurig/TclHaskell/