Haskell, with its support for pattern matching on data structures, generic structure traversals, and expressive type system, is popular for implementing compilers and intepreters. Here's a selection of languages implemented in Haskell.

Large languages

Haskell

GHC: GHC, The Glasgow Haskell Compiler, is written in Haskell

Yhc: Yhc, The York Haskell Compiler, is written in Haskell

Jhc: Jhc is a Haskell compiler which aims to produce the most efficient programs possible via whole program analysis

nhc98: A compiler for Haskell 98, written in Haskell

pH: A parallel version of Haskell from MIT.

Perl

Pugs: Pugs is an implementation of Perl 6, written in Haskell. It aims to implement the full Perl6 specification.

Ruby

RType: RType is a Ruby interpreter written in Haskell

Scheme

Write Yourself a Scheme in 48 Hours: A Haskell Tutorial.

Emacs Lisp

Helisp: The beginnings of an Emacs lisp compiler/interpreter.

Epigram

Epigram: Epigram is a prototype dependently typed functional programming language

Curry

[http://danae.uni-muenster.de/~lux/curry/ The M�nster Curry Compiler]: A native code compiler for the declarative multi-paradigm language Curry, written in Haskell

Bluespec

Bluespec: A compiler for a hardware description language translating a Haskell-like (but with System Verilog syntax these days) language to Verilog.

Small languages

Baskell

Baskell: An interpreter for a small functional programming language. Supports strict and non-strict evaluation, and type inference. Useful for teaching purposes.

Unlambda

Unlambda.hs: An implementation of unlambda in Haskell

BF

BF.hs: An implementation of BF in Haskell

Untyped lambda calculus

LMEngine: An implementation of the untyped lambda calculus

This page contains a list of libraries and tools in a certain category. For a comprehensive list of such pages, see Applications and libraries.