0 A.D. - 0 A. D. is a free, open-source, historical Real Time Strategy (RTS) game currently under development by Wildfire Games, a global group of volunteer game developers. Download 0 A. D.
OpenTTD - An open-source clone of the classic game ...
Age of Empires - Age of Empires is the critically acclaimed, award winning Real Time Strategy (RTS) game with a legacy spanning over 20 years and nearly a dozen titles in the franchise.
Micropolis - Micropolis is the open source version of SimCity Classic from Maxis, developed by Will Wright and Don Hopkins.
openage - Free Age of Empires II clone
Simutrans - Simutrans is an open-source transport simulator.