University directory of /forth/gforth. Many fine resources.

Full GNU Forth manual, linked Table of Contents. On website of one of Gforth developers.

For GNU Forth: MyUnits (Java-like units) library, forth sources, links.

Free, fast, portable implementation of ANS Forth, on GNU website. Works well with Emacs editor. Many nice features: input completion and history, powerful locals facility, object oriented aspects. Employs traditional implementation methods: inner interpreter indirect or direct threaded.