Marathon is the first part of a trilogy of first person shooter games. The game takes place in the 2794 aboard a large, colony spacecraft called the UESC (United Earth Space Council) Marathon. The game follows a superhuman cyborg who must work to free the spacecraft from hostile extraterrestrial slavers called the Pfhor.
The sourcecode to Marathon 2 was released by Bungie in 1999. The sourcecode was adapted into an open source project called AlephOne. In 2002, a group of fans created a remake of the original Marathon using the Marathon 2 engine called M1A1. In early 2004, Bungie released the entire Marathon Trilogy as freeware, allowing it to be downloaded free of charge.
DCEvolution released a Dreamcast image that contains all three games in the Marathon trilogy. This image can be used with any program which recognizes DiscJuggler images to create a CD-R of the game which boots on the Dreamcast. The Dreamcast port of AlephOne requires a Dreamcast keyboard.