[ANTLR] is a tool for building parsers, language translators and compilers.
The [Catalog of Free Compilers] is a list of freely available software for language tools, which includes the following: compilers, compiler generators, interpreters, translators, important libraries, assemblers, etc. -- things whose user interface is a language. Natural language processing tools may also be included.
Jack Crenshow's [Let's build a compiler] is a great introduction for non-technical on how to hand build a compiler.
[ToonTalk] is an animated visual programming environment for children.
A native windows port of [Flex and Bison]. This site also has an html version of the man pages.