Along with the OpenMW[1], OpenRA[2], OpenTTD[3] and OpenRCT2[4] listed on openage's GitHub page, lots of others exist. To name a few:
* OpenXcom[5] for X-COM: Enemy Unknown and the later Terror From the Deep games.
* Nuvie[6], Exult[7] and Pentagram[8] for Ultima VI-VIII respectively.
* GZDoom[9] (and various others) for running Doom, Doom II etc.
* Freeciv[10] for running Civilization.
[6] http://nuvie.sourceforge.net/
[7] http://exult.sourceforge.net/
[8] http://pentagram.sourceforge.net/