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) on the level Tsavo Highway, 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 used this build to finish the final details of the game. It was over on the 29th of August, when Halo 3 went gold.