Chameleon

Haskell-type language, implements ideas described in a 'A Theory of Overloading'. Compiles Chameleon to (plain) Haskell; can mix Haskell and Chameleon overloading. Descriptions, documents, downloads.
http://www.comp.nus.edu.sg/~sulzmann/chameleon/

Data Field Haskell

Dialect with instance of data fields (a generalization of arrays), useful for rapid prototyping of parallel algorithms, and parallel high-level system specification.
http://www.mrtc.mdh.se/projects/DFH/

Eden

Extends lazy functional language Haskell, but overrules lazy evaluation whenever needed to support parallelism; gives programmers enough control to implement parallel algorithms efficiently, and frees them from low level details of process management.
http://www.mathematik.uni-marburg.de/inf/eden/

nhc98 from York

A Haskell 98 compiler.
http://www.cs.york.ac.uk/fp/nhc98/

Mondrian

Light version of Haskell to interoperate with other languages in OO environments; runs on .NET (old version for JVM), supports ASP.NET, to embed functional code in webpages with C#. Has version of Glasgow Haskell Compiler using Mondrian for .NET system to
http://www.mondrian-script.org/

Jaskell Project

Java bytecode generator backend for Glasgow Haskell Compiler (GHC), so one can build Java applets or applications via the Haskell language.
http://www.scdi.org/~avernet/projects/jaskell/

pH (MIT parallel Haskell)

A parallel eagerly evaluated variant of Haskell with syntactic provisions for loops, barriers, and I- and M- structure storage.
http://www.csg.lcs.mit.edu/projects/languages/ph.shtml

The Glasgow Haskell Compiler (GHC)

An optimizing compiler for Haskell, written in Haskell. Includes extensions for concurrency and heap & time profiling. [Open Source, BSD-like]
http://www.haskell.org/ghc/

Template Haskell

Haskell 98 extension allowing type-safe compile time metaprogramming, with Haskell, as the manipulating language and the language being manipulated.
http://www.haskell.org/th/

Distributed Haskell

Extension for parallel and distributed programming, with combinators from concurrent constraint programming; computational parts of programs are expressed functionally, development was first for tightly coupled multiprocessors, evolved from Goffin.
http://www.cse.unsw.edu.au/~chak/goffin/

Helium

A functional programming language (subset of the Haskell) and a compiler designed especially for teaching Haskell.
http://www.cs.uu.nl/helium/

Hugs

An interpreter for Haskell which runs on almost any platform. Primarily used for teaching.
http://www.haskell.org/hugs/

Haskell++

Object-oriented Haskell extension, using a preprocessor, supports a form of inheritance via extended class and instance declarations. Descriptions, documents, source download, links.
http://www.cs.chalmers.se/~rjmh/Software/h++.html

Hugs Archive

Many files for Hugs Haskell interpreter: source code, documents.
http://www.cse.ogi.edu/~mpj/hugsarc/

O'Haskell

Object Haskell: Haskell conservatively extended with subtyping, monadic objects.
http://www.cs.chalmers.se/~nordland/ohaskell/

Glasgow Parallel Haskell (GpH)

A Haskell extension for parallel programming built on top of the Glasgow Haskell compiler (GHC). Parallelism is identified using annotations (generally evaluation strategies), that are defined using only two extra primitives: par and seq.
http://www.cee.hw.ac.uk/~dsg/gph/

The HBC compiler

A compiler and interactive system for Haskell 1.4, unsupported for two years now.
http://www.cs.chalmers.se/~augustss/hbc/hbc.html

Gofer

Small interpreter for language based on Haskell report 1.2; experimental, more so for type classes. Haskell adopted some ideas of Gofer, but Gofer type class system is more flexible. Runs on DOS, Linux, Macintosh, Unix. Hugs predecessor.
http://www.cse.ogi.edu/~mpj/goferarc/

PolyP

Polytypic programming language; source files for compiler written in Haskell that compiles PolyP-code to Haskell; library of polytypic functions written in PolyP, some examples, documents, downloads.
http://www.cs.chalmers.se/~patrikj/poly/polyp/