Lambda Wars (formerly Half-Life 2: Wars) brings the struggle between the human resistance and their Combine overlords to a multiplayer real-time strategy setting. The Lambda Wars beta only requires Alien Swarm installed to play. It features 3 multiplayer game modes: Sandbox, Annihilation and Overrun, showcasing the Rebels and Combine playable factions and a full-fledged RTS interface and HUD. There is also a singleplayer tutorial and a handful of singleplayer missions.
Wow... just played for about 3 hours and i can already tell you guys that this is a mod done right. Im mean of course is still on beta but damn this is a hell of a fun mod. So right now you can only play with 2 armies which is the rebels and the combines, each one different in alot stuff like constructions and units, i prefer the combine because they have some freaking awesome units. If you're looking to buy an RTS game look no further, this is a hidden gem for free and more people should play it.