Alien Swarm is a total conversion mod for Unreal Tournament 2004 created by Black Cat Games and initially released on May 28, 2004. Alien Swarm, version 1.2 was released on September 10, 2004, with the official campaigns, Sigma and Ortega. Alien Swarm version 1.3, together with a third campaign, Telic, also introducing new weapons and items, plus some bug fixes was released on December 16, 2005. On February 13, 2007 another new campaign and the version 1.32 patch were released. On January 31, 2010 version 1.34 patch was released, adding widescreen support.
In Alien Swarm, the player assumes the role of a commander in the Interstellar Armed Forces and uses the unique skills of the marines at his disposal to fight through infested space ships and colonies that have been overrun by aliens. Alien Swarm can be played both offline and online with up to eight people each controlling one of the eight unique marines. Each marine falls into one of four classes: explosives, special weapons, technical, or medic. The game can be played either as single missions or as a series of missions called a campaign.
There are currently 2 official campaigns for Alien Swarm, Sigma and Ortega, as well as the Phalanx Campaign created by MjrHuRTz and Upsilon Campaign. The Telic Campaign added new weapons, items, and maps to the game. A sequel to the Telic Campaign, Escape From Rhea, brought more weapons, equipment, and maps to the game. There are also a number of fan made maps and a mutator that allows players to string together a series of maps into a custom campaign.
Alien Swarm was the winner of Phase 4 of the Make Something Unreal Contest for best non-FPS modification. The mod was also a finalist in the MSUC for the grand prize of an Unreal Engine license, eventually won by Red Orchestra. The mod was also declared Mod of the Year by GameSpy.