omega is a complex rogue-style game of dungeon exploration. Unlike other such games, there are a number of ways to "win", depending on various actions taken during play. The ways you can get your name on the hiscore board include becoming the highest ranked head of a guild, sect, college, etc., as well as gaining the most points figured from possessions and experience. The game (via the oracle) may impose some structure on your exploration, but you need not follow all of the oracle's advice. There *is* a "total winner" status, by the way.
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.