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.
Stronghold - Stronghold Crusader is a RTS game from the series from Stronghold.
Simutrans - Simutrans is an open-source transport simulator.
ANNO - ANNO is a city-building and economic simulation video game series, with real-time strategy elements.