DGD

Dutch programmer Felix Croes, known as Dworkin, wrote DGD in the early 1990s without starting from LPMud's code. The result was a leaner driver with its own LPC dialect and few assumptions about what sort of game would sit on top. Where other drivers shipped a full toolbox, DGD left almost everything to the mudlib.

Its signature feature was persistence. DGD can dump its entire memory image to disk and resume exactly where it left off, and it can recompile objects in a running world without losing their state. That made it interesting to commercial outfits too — Skotos built its storytelling games on it. It is the same idea that much later gets pitched as "hot reload".