For those who don't know Empires Mod is a mod for Half Life 2 ,or any other Source engine game, that makes it into an RTS. Basically there are two teams, and one commander for each team. The commander controls where things are built and what gets upgraded, he can also reccomend targets to his team-mates. The rest of the players are fighting FPS style, as either a Gredinier, Engineer, Rifleman, or Scout.
Each class has its ups and downs, Riflemen can take out infantry easily, Engineers can build powerful turrents, Scouts can snipe important targets, and the Gredinier can take out armored targets. The game is really fun, you can download it here: http://www.empiresmod.com/