A project I've been working on, on and off over the years is Gigalomania ( http://gigalomania.sourceforge.net/ ), a Mega Lo Mania like RTS where you develop weapons and conquer your enemies, advancing through the ages from the stone age to the future!
It's available for Windows, Linux, OS X, Android and more. The game is GPL v2 or later, with assets released under various Free licences.
An earlier version was featured on Free Gamer blog ( http://freegamer.blogspot.co.uk/2013/03 ... dates.html ). Since then there have been bug fixes, tweaks to the gameplay, tutorials added, speech samples and music, and improvements to the graphics.
It could still do with graphical improvements (e.g., the buildings which are rather simplistic and lack varation; defender sprites; or general overall consistency), but it's improving slowly Please let me know if anyone wants to help out with graphical improvements.