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Aleph One is an enhanced open source version of Marathon 2: Durandal's game engine.[1] The game engine has been in development since the year 2000 when Bungie released Marathon 2's source code prior to its acquisition by Microsoft.


The game engine has made many improvements to Marathon 2, such as: OpenGL rendering, high-resolution graphics, frame rate interpolation (to raise the games beyond their original 30 fps), programmable shaders, fully-3D entities, Lua scripting, various internal changes allowing for more advanced mods, and Internet-capable multiplayer (whereas the original games had only LAN capability) with the use of a matchmaking server to organize games.


Prior to the release of Marathon Infinity in 1996, fans used fan-built tools to create custom maps, sounds, physics, and shapes that they shared amongst themselves for Marathon and Marathon 2. Seeing how much fans enjoyed creating their own maps and files, Bungie released Marathon Infinity with an official editing tool, Forge, allowing fans to fully modify the game.

While it's not known why (perhaps due to the popularity of Forge), Bungie released the source code to the Marathon 2 engine under GNU GPL-2.0-or-later in the year 2000. It was here where Aleph One began.

Five years later, Bungie authorized the release of the entire Marathon Trilogy to be freely distributed,[2] which let Aleph One develop the trilogy to be played for free on any supported platform.

To celebrate Bungie Day 2011, 'Marathon Man' Daniel Blezek released a version of the original Marathon for Apple's iPhone and iPad for free using Aleph One's engine.[3] He eventually released the remaining games on Apple's App Store.[4]

In March 2024, it was announced that the entire Marathon trilogy would be released on Steam under Aleph One,[5][6][7] with the first game retitled as Classic Marathon.[8]