Revamping the developer's classic 'Alien Breed' series, Impact features two-player co-op, upgradeable weapons and hordes of aliens to blast. It was released first on Xbox 360 as Alien Breed: Evolution then "expanded" for PC and PlayStation 3 as Impact.
Selling a top-down shooter on Steam can't be easy when the illustrious Valve's offering its own--Alien Swarm--for free but offering a 50% discount certainly should help. The offer runs until Thursday, August 5 and a demo is available for you to try before you buy.
I thought Alien Swarm was free...oh wait.