Im playing the new remake of
total annihilation, well its not that new but its still new enough :P. I dont understand though, not that many people seem to know about it.
BUT IT COMPLETELY FREE! 
The engine that it uses is called "Spring". You can download many mods for it, in my opinion XTA (9.45 latest version) is the best as it is almost exactly the same as the old TA game but with updated 3d graphics.
you can download the client and the mods here.
The Spring Project
it can be abit tricky to understand the client at first, u need to make a username before it will log you in, but you do all that in the client options.
Give it a go!