Darker Realms

From the official website:

Darker Realms is a multi-user text-based adventure game (aka MUD) with a primarily medieval theme. Operating since June of 1990, it was one of the first LPMuds to open, and is the oldest continually running LPMud in the United States and the second oldest in the world. It was also the first MUD of any kind to feature a quest-based advancement system. DR still maintains many of the classic elements of an LPMud, as well as several very unique guilds, original and enjoyable quests of varying difficulty, text versions of over a dozen card and board games, and a good number of more modern features such as built-in colors and aliases.