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.
OpenRA - What if Albert Einstein changed history? What if the Andromeda Strain were a miracle mineral?
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.
Dune Legacy - Dune Legacy is an effort by a handful of developers to revitalize the first-ever real-time strategy game.
openage - Free Age of Empires II clone
Stronghold - Stronghold Crusader is a RTS game from the series from Stronghold.