Halo 3 Epsilon

Halo 3 Epsilon was an internal-only Halo 3 build. It was released to Microsoft employees as of August 10, 2007, and featured Campaign (both single-player and cooperative gameplay) on the level Tsavo Highway, as well as Forge and multiplayer on six maps: Epitaph, High Ground, Last Resort, Sandtrap, Snowbound, and Valhalla.

Halo 3 Epsilon was confirmed to some degree later on August 10th, 2007 by Bungie Studios on a Bungie Podcast. Microsoft employees, Xbox.com representatives, and the Bungie Studios staff played it, and Bungie employees used this build to finish the final details of the game. It was over on the 29th of August, 2007, when Halo 3 went gold.

Epsilon had several features not seen in the game, such as being able to spawn Shade turrets and Deployable Lookout Towers in Forge. This can be seen in older Halo 3 leaked footage, and the two aforementioned items have been modded into some multiplayer maps, all of them part of the Epsilon set.

Trivia

 * An anonymous US gamer using the gamertag "Scar" managed to unwittingly download Halo 3 Epsilon. He played the game with his console connected to Xbox Live, and quickly came to the attention of Microsoft. On September 2007, his gamertag and console account were banned until December 31, 9999.
 * In the Halo 3 Epsilon version of Tsavo Highway, Sergeant Stacker's radio com emits no static. This may be because it wasn't added in until later, or it was a glitch Bungie was still attempting to fix.