Unvanquished is an open-source FPS game featuring team-based strategy and RTS elements, pitting humans against aliens in a futuristic setting.https://forums.unvanquished.net/
https://forums.unvanquished.net/viewtopic.php?t=1379
http://youtu.be/Q3hV1PtxQAw or http://vimeo.com/87519514