Aleph One is the open source continuation of Bungie's Marathon 2 game
engine. Available for Mac OS X, Windows, and Linux, Aleph One supports
Marathon 2 and Marathon Infinity natively, and Marathon through a
conversion called M1A1. Many third party scenarios and net maps are
also available.

Aleph One is available under the terms of the GNU General Public License
(GPL).

Aleph One is just a game engine. The game data from at least one of
the Marathon series is required to play. Install one or more of
marathon-data, marathon2-data, and/or marathon-infinite-data.

See the READMEs for the game data packages for more information.