As promised, Valve has released top-down co-op shooter Alien Swarm on Steam, free of charge. Have fun! https://kotaku.com/valve-unleashes-an-alien-swarm-on-steam ...

The minute players step into one of the tactical shooterDarkSwarm's procedurally generated missions, they are confronted by the titular Swarm: parasitic aliens who take a variety of forms. The Swarm ...