Shooter Alien Swarm has become the latest title to get a Source engine revamp – and Valve has chosen to give it away over Steam.
The original Alien Swarm was released as a mod to Unreal Tournament and the team behind, who call themselves Black Cat, were acquired by Valve in 2008. The team was involved in the production of acclaimed zombie shooter Left 4 Dead 2.
Also available for download will be the game's code base – a move that Valve no doubt hopes will encourage the next generation of coders to show off their skills.
Alien Swarm was released over the weekend and allows for four-player co-op, including over 40 weapons and four character classes.