Gforth is a fast and portable implementation of the ANS Forth
language. It works nicely with the Emacs editor, offers some nice
features such as input completion and history and a powerful locals
facility, and it even has a manual. Gforth employs traditional
implementation techniques: its inner innerpreter is indirect or
direct threaded.

WWW: http://www.gnu.org/software/gforth/gforth.html