@beardalaxy @BlinkRape There is also O.H.R.RPG.C.E. (Official Hamster Republic Role Playing Game Construction Engine) (dumb name and acronym) which is FOSS, but it seems to be only suited for NES/SNES style RPGs.
https://rpg.hamsterrepublic.com/ohrrpgce/Main_Page
You also have Solarus which is basically the RPG Maker equivalent for Zelda-clones. It supports Lua scripting and is FOSS.