It was added to Steam Greenlight on 3rd September 2012 and later added to Steam Early Access on Its multiplayer is in development which will lay a foundation for its larger singleplayer/co-op campaign.
It was added to Steam Greenlight on 3rd September 2012 and later released on Steam's Early Access platform on July 2nd, 2013. The multiplayer is being developed first to lay a foundation for the larger singleplayer/co-op campaign.