Halo 3 Epsilon

Halo 3 Epsilon is an internal-only Halo 3 build.

It was released to Microsoft employees as of August 10, 2007, and featured campaign (single-player and cooperative gameplay both), Forge, and multiplayer modes.

Halo 3 Epsilon was confirmed to some degree later on August 10th by Bungie Studios on a Bungie Podcast. Microsoft employees, Xbox.com representatives, and the Bungie Studios staff have been playing it, and Bungie employees are using this build to finish the final details of the game.