OpenTTD - An open-source clone of the classic game ...
Tropico - Tropico is an Addictive, Strategy, Construction and Management, City Building, Sandbox and Single-player Simulation developed by PopTop Software.
Micropolis - Micropolis is the open source version of SimCity Classic from Maxis, developed by Will Wright and Don Hopkins.
ANNO - ANNO is a city-building and economic simulation video game series, with real-time strategy elements.
Simutrans - Simutrans is an open-source transport simulator.
Stronghold - Stronghold Crusader is a RTS game from the series from Stronghold.