ANNO - ANNO is a city-building and economic simulation video game series, with real-time strategy elements.
Wren - Offset your carbon footprint by saving rainforests
Stronghold - Stronghold Crusader is a RTS game from the series from Stronghold.
YAYZY - Track the carbon footprint of each purchase in real-time
The Settlers Online - The Settlers is a free web browser based strategy game along with a gameplay that drops anywhere between Age of Empires and the online strategy style.
Klima - Go carbon neutral