“0 A.D. (pronounced “zero-ey-dee”) is a free, open-source, historical Real Time Strategy (RTS) game currently under development by Wildfire Games, a global group of volunteer game developers. As the leader of an ancient civilization, you must gather the resources you need to raise a military force and dominate your enemies.”
Source 1: http://play0ad.com/
Thank’s I read about it ad instantly forgot about the link! I already gave up searching for it. Perfect timing!