lbForth

One compelling use case is getting a REPL on any microcontroller with a UART and, say, ≥64K RAM (I remember lbForth[1] being particularly portable, and there are other implementations you could use as well). I don’t know if you’d want to have that be your first experience with the Forth itself, though: there’s inherent fiddliness involved in bringing up hardware; the win is that Forth doesn’t really add any of its own once you’re vaguely familliar with the internals. If you can get it to boot and send and receive bytes, you can get an interactive Forth on it—or if the available resources don’t permit that, on an imaginary machine spanning it and your PC (a “tethered” Forth). [1] https://github.com/larsbrinkhoff/lbForth

My personal Forth can write Linux ELF and Windows PE executables. (I don't have access to a Mac, so OS X Mach-O is out.) http://github.com/larsbrinkhoff/lbForth