From HaskellWiki

People often ask, «Okay, Haskell looks like a fun language; but what's written in it?»

The purpose of this page is to create a list of Haskell-based projects.

Requirements

To qualify, the project should meet these requirements:

Programs, not libraries The project should be of value to the end user. Programs that are configured by writing a small piece of Haskell code (xmonad, yi) or that expose a Haskell-based DSL are okay. A significant part is written in Haskell As a rough guideline, no less that 30% of the source code should be Haskell. Open source Not necessarily «free as speech», but people should be able to try it out and look at the source code. Valuable outside of the Haskell community Haskell infrastructure is almost entirely written in Haskell, but that isn't very useful in selling Haskell to outsiders. Tools that work with other languages (e.g. a Perl6 implementation written in Haskell) are okay. Successful The project should be maintained and have a non-trivial user base.

Projects