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/

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/

Eden
   Parallel functional language to program reactive systems and parallel algorithms using distributed memory. Extends Haskell, but overrules lazy evaluation whenever needed to support parallelism; gives enough control to implement parallel algorithms efficie
   http://www.mathematik.uni-marburg.de/~eden/

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/

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://web.cecs.pdx.edu/~mpj/goferarc/

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

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/

Hugs Archive
   Many files for Hugs Haskell interpreter: source code, documents.
   http://web.cecs.pdx.edu/~mpj/hugsarc/

Hugs98 for .NET
   Extension of Hugs98 Haskell interpreter, for interoperation between Haskell and .NET and its framework; can instantiate and use .NET objects in Haskell, and vice versa, call and use Haskell functions from any .NET language.
   http://galois.com/~sof/hugs98.net/

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/

Kahu Research
   Makes Mondrian, light Haskell version 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 .
   http://kahu.zoot.net.nz/

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

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/

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/

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/

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

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

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