Halo 3: ODST

Halo 3: Keep It Clean is a campaign expansion to Halo 3. It takes place in Mombasa, Kenya, presumably during the events of the First and Second Battle of Earth.

Overview
Although Bungie has consistently stated that Halo 3 was the last game in the trilogy, having ever ruled out possible Halo games in the same story line being released in the near future, an interview by MTV with Don Mattrick (Senior Vice President of Microsoft's Xbox division) revealed that Bungie's game is at the very least Halo-related, and that it is not Bungie's collaborative efforts on Halo Wars or Halo: Chronicles, but a "new" game.

Although a proper announcement was meant for July 16th, 2008 at E3, it was canceled by Microsoft because they wanted to focus on games by first-party developers that were coming out in 2008 - criteria which the Bungie project did not fit. It was also stated by Microsoft that they did not want to further lengthen their press conference so as not to stretch the attention span of the attendees, and that they wished to give the new Halo project an event of its own to release details on it.

The most popular rumor surrounding this new title is that it's a squad-based shooter in the Halo universe with the player filling the role of a Marine commander. This could be the reason why Christian Allen, a former Marine and Red Storm employee who worked on the Ghost Recon and Rainbow Six series, joined Bungie in early 2007.

In a section of the video, what appears to be random letters and numbers contains the possible release date for the game.

Trailer
First, different screens of areas of New and Old Mombasa come on screen, followed by HEV pods entering the atmosphere. Here you can see the Prophet of Regret's carrier on the right, then it moves behind buildings. The pods come into view as a large EMP explosion (Caused by the Prophet of Regret's carrier entering Slipspace) appears, sending the pods off-course. Then, the Superintendent appears, and shows warning signs and then reboots. All the screens from earlier flash onto the screen, but heavily damaged from the blast. Then, a single HEV pod falls through the sky, when the Halo 3 Logo appears. The pod then crashes into the camera and goes black, followed by the words 'Prepare to Drop'.

Trivia

 * A teaser trailer for Keep It Clean was released at 07:07:07 am PST on September 25th, 2008, the one year anniversary of Halo 3. The trailer was viewed through the many security cameras around New Mombasa.
 * The final words "Prepare to Drop" may refer to the Helljumpers who use Human Entry Vehicles to drop to the surface. This may mean that the expansion may take place from the point of view of a Helljumper.
 * When "Halo 3" is displayed in the font similar to Courier, by slowing down the video someone can see the words : "Activating sub-routine “Vergil". Warning, Data Leak on Level 9"
 * When the camera switches to the street with the 2 cars before the blast, it reads in the right corner: SIERRA117 LOC LINK 0x2F278609. It seems that the Superintendent is looking for or displaying John-117's coordinates.