Marathon Infinity is a first-person shooter video game, the third in the Marathon Trilogy of science fiction by Bungie. The game was released on October 15, 1996 and included more levels than its predecessor Marathon 2: Durandal. These were larger, and formed part of a more intricate plot that spanned both space and time. Marathon Infinity, unlike Marathon 2, was originally released only for the Apple Macintosh. However, Bungie released the source for Marathon 2 in 1999, allowing the development of the open-source Aleph One engine. In 2005, Bungie released the trilogy to the public as freeware, allowing the games to be freely downloaded. In 2011, Bungie released the source code for Marathon Infinity itself.