ALLEGIANCE

"Most multiplayer games exhibit a very simplistic concept of teamwork, if any. Allegiance is a 3D space shooter/sim in the tradition of X-Wing vs Tie Fighter that goes far beyond any similar efforts in this arena. With support for up to 58 players in small game mode and 200 players in big game mode, eight different factions each with five distinct research paths, several different categories of spacecraft, a dedicated commander position with an RTS style 3D interface and a gameplay style that demands coordinated teamwork to accomplish anything, Allegiance goes where no multiplayer game has ever gone before."

It's free as well :-)

I just lost half an hour to this.