SunAge was developed by Vertex4, and aims to go back to the roots of the real time strategy genre, using detailed 2D art and an isometric viewpoint. It was originally released for Mac in 2007, and got an updated port for Windows 8 PC's and tablets in early 2013.
Following a successful Greenlight application, the game was released on Steam on December 15, 2014.
The Federation is what's remaining of the somewhat civilized world, now residing in domed cities as nuclear war has turned Earth into a place inhospitable to life.
The Raak-Zun is what became of the humans who weren't let into the city domes, forced to survive in the radioactive wastelands they became mutants, and formed scavenging tribes.
The Sentinels are an alien species, invading Earth using inter-stellar portals.