free forth compilers
Bigforth is a native code Forth originally developed for the Atari ST. The current version runs on Windows 95/98/NT and Linux. It is released under the GNU GPL. It generates optimised native code for the Intel i386 and has a number of tools included: multitasker, decompiler, source level debugger, and editor. A huge library is included and separate compilation is also supported.
Gforth is GNU's Forth compiler, and like many of the GNU tools, it is portable to a number of systems. It implements the ANSI Forth language.
4th is a compiler-cum-interpreter that handles Forth-like source code. The website claims that it is able to compile most Forth programs. The intermediate code generated can be run by the interpreter.
Atlast is an embeddable FORTH-like language, originally developed by Autodesk, Inc, and is based on the FORTH-83 language with numerous extensions. It is portable to MSDOS, OS/2, Macintosh, and many Unix systems.
Forth compiler with OO extensions designed to be embedded into other programs or systems. Ficl has a small memory footprint, and is very quick to port to 32 bit or greater systems with a Standard C runtime. BSD license.