[astrobe_]

This is made by the company the inventor of the language created. Then he left it because Forth, inc. needed the language to be standardized, which wasn't his idea of Forth and, his point of view is that he solved the software problems and what was left was solving the hardware problems, so he moved to working on stack-based processors.

Swift Forth is literally a professional Forth and is well regarded. The other often recommend Forth is the FOSS GForth. They are good for starting because they are popular and standard, so you'll find help easily.

Other "smaller" Forth are often non-standard dialects and are more-or-less mature experiments.