QuakeC

John Carmack built a small virtual machine into Quake (1996). Everything to do with rules — weapons, monsters, doors, scoring — lived in QuakeC source compiled by qcc into a single progs.dat. id published the game-logic source, and anyone could change it and run the result on any platform without touching the engine.

The language was spartan: the types were essentially float, vector, string and entity, and there were no arrays. It was still enough for Team Fortress and hundreds of other mods. Quake II switched in 1997 to game logic in an ordinary loaded DLL — faster, but without the sandbox or the portability.