MAngband is a free online multiplayer real-time roguelike game, derived from the single player game Angband.

To win the game you must build up a character, selected from any one of 10 races and 6 classes, to be powerful enough to defeat Morgoth, Lord of Darkness, who lives in the dungeon 5000 feet below the surface of the town. As you work towards this near-impossible goal, you will chart unexplored dungeon passageways, do battle with legendary creatures, and find lost artifacts. And of course throughout your journeys you will encounter many other adventurers -- whether they be friend or foe is up to you to decide!

License: free

Additional System Requirements: Should compile fine on any system with a termcap library (NCurses, Curses), or an X11 distribution.
(Hint for Linux: Remove the -ltermcap entry in the Makefile to get it to compile -lncurses should be all that's needed on Linux systems)