NannyMUD is an LPMUD started in April of 1989. It is widely considered to be the oldest continually running MUD based on the LPMUD 2.4.5 library.
It is a multi-player text-based adventure game. Players of the game are allowed to program their own additions to the game in a language called LPC, after they have advanced sufficiently within the game. This is typical of LPMUDs.
It is one of many LPMUDs, but is notable because of its age and history. Additionally, the programming language pike
evolved from NannyMUD's particular take on LPC