Xonotic

A direct successor of the Nexuiz Project, Xonotic is a free, open source (GPL) shooter game that serves as the updated and much improved version of the former. After internal disagreements plagued the Nexuiz Project, several developers took a stand and vowed to remake the game from scratch. Creating one that's even better and ensuring that it'll remain free with an open source license. The game was created by a team of "players, developers, and artists who enjoy learning and refining their skills through contribution and collaboration with other players from around the globe." Thanks to this effort, this forked version features much of what gamers could hope for. With stunning graphics, engaging gameplay, great maps and a host of other features; Xonotic is slowly shaping up to becoming an excellent game.