I feel compelled to drop this game here, because it's the best game you've never played.
It's much like Natural Selection 2 (but way more complicated, and the GUI is unfortunately far less intuitive). One player plays as commander and makes RTS-like decisions, while all the players will play as the units in a space combat game.
Beware though, the learning curve (and setting the keybinds) are rough.
Free on steam, starting tonight at 6 PM Eastern.
http://store.steampowered.com/app/70048 ... llegiance/