Crossfire is a multi-player graphical arcade and adventure game made for X. It has certain flavours from other games, especially Gauntlet and the rogue-like games (Nethack, Moria, Angband, and Ragnarok). Any number of players can move around in their own window, finding and using items and battling monsters. They can choose to cooperate or compete in the same world.
Slash'EM (Super Lotsa Added Stuff Hack -- Extended Magic) is a variant of the hugely popular roguelike game NetHack. It adds more monsters, more objects, more dungeon levels, more roles, and more races, shopkeeper services, and techniques for you to use, and invisible objects and gypsies for those who feel lucky. It also comes with a GTK windowing interface and higher resolution tile sets as options.
TinyMARE (Multi-user Adventure Roleplaying Epic) is a text-based MUD server completely rewritten for efficiency using TinyMUSH and TinyMUSE as a basis for its game engine. The server is designed for creating an extensive, novelistic role-playing atmosphere supporting real-time combat, day & night, seasons, and global weather. Using a telnet client, players can log on to explore a virtual world, find magical items, learn skills and techniques, and group together to surpass obstacles you create in your own epic adventure.