That's a completely different kind of game. Roguelikes are single-player games, MUDs are multiplayer games. Roguelikes usually feature permadeath, MUDs rarely do. It's the difference between an RPG and a MMORPG.
Also Nethack offers a turn based top down gameplay simulated with ASCII chars, MUDs are real time or almost real time based with a wall of text and prompt based, like a text adventure.
