Favored Freeware: Aleph One

Aleph One is an open-source descendent of Bungie’s classic first-person shooter trilogy, Marathon. Aleph One features OpenGL rendering and supports Marathon 2 and Marathon Infinity data files. A conversion of Marathon 1, called M1A1, and many third party scenarios are also available.

Pros: Aleph One’s support for OpenGL and optional high-resolution textures and landscapes breathes new life into the classic Marathon Trilogy. Aleph One is a cross-platform game for Mac, Windows, and Linux.

Cons: None significant.

Note: The story of the Marathon Trilogy continues in the unofficial fourth installment, Rubicon X.