UFO: Alien Invasion is a computer game in which the player fights aliens that are trying to take control of the Earth.
The game is heavily influenced by the X-COM series, mostly by X-COM: UFO Defense. It is based on a modified id Tech 2, and runs on Linux, Microsoft Windows, and Mac OS X for both PPC and Intel Macs. It was nominated for "Best project for Gamers" in the Sourceforge 2007 and 2008 Community Choice Awards.
Most aspects of the game are still in an evolutionary development, but it should be considered a fully playable game. Currently, version 2.2.1 is the most up to date version (released 29 April 2008). Licensed under the GNU General Public License, UFO: Alien Invasion’s engine is free software, but it includes media under other licenses, including the non-free CC Sampling+. Development is coordinated through SourceForge.net.