pfe ("portable Forth environment") was the first one I used; it was included in Slackware96 and included a Tetris game. You're probably aware GForth, BigForth, and F-83 are mostly written in Forth. I recently read through Retro-Forth, which compiles to an interpreter for a bytecode called Nga, written in C. There was another one I ran into recently but can't find now... aha, SOD32: https://lennartb.home.xs4all.nl/forth.html