you are looking for LPmuds.

LPC is a language that looks like C (the C in LPC) and there is even a general purpose language called pike that is a rewrite of LPC.

in an LPmud, the engine and the world itself including user contributed part are all written in LPC. unlike other MUDs that have a core written in C and an obscure custom language to define the world inside. this made LPmuds very approachable, and i believe the language and architecture is what enabled LPmuds to have built-in ftp and later webservers too, all written in LPC.