Hugs is a small, portable Haskell interpreter written in C runs on almost any machine. Hugs is best used as a Haskell program development system: it boasts extremely fast source code interpretation, supports incremental interpretation, and has the convenience of an interactive...
Hugs is no longer in development. Last version, released in September 2006, is still downloadable from the official website.
UHC is a Haskell implementation from Utrecht University. UHC supports almost all Haskell 98 and Haskell 2010 features plus many experimental extensions. The compiler runs on Mac OS X, Windows (Cygwin), and various Unix flavors.