It was announced today via this Steam Community posting that Robocraft has been ported to Linux and OS X and that these ports will soon be released on Steam. "We have completed the work to get the Mac and Linux versions up and running and they are in test now and will launch very soon via Steam." Robocraft is powered by the Unity Game Engine.
Robocraft is self-described as "If Minecraft smashed straight into World of Tanks you'd get Robocraft. BUILD, DRIVE & FIGHT in this Free-To-Play MMO Robot vehicle shooter. Build a robot battle vehicle, add wheels, jets, guns, wings and take it into intense online team battles."
Those wishing to learn more can stop by the Steam Store (it's free to play) or watch the game trailer embedded below.