UFO: Alien Invasion

UFO: Alien Invasion is a strategy video game in which the player fights aliens that are trying to take control of the Earth. The game was heavily influenced by the X-COM series, especially UFO: Enemy Unknown. It is based on a heavily modified Quake II engine, and runs on Linux, FreeBSD, OpenBSD, Microsoft Windows, AmigaOS 4, and Mac OS X for both PowerPC and Intel Macs. There is also a version for Android, published on Android Market.