robocraft

RoboCraft is a Free-to-play multiplayer action sandbox game. It is a combination of two very popular and successful games Minecraft and World of Tanks. You build your own robots battle vehicle, add wheels, guns and rocket and fight other players.

Developer have posted on steam community that it will be releasing on Mac and Linux.

http://steamcommunity.com/games/301520/announcements/detail/201854770784767225

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.

This game is created with Unity 3D. Nice to see more Unity3D games are getting released on Steam and Linux.

Publisher: Freejam
Developer: Freejam
Genre: Free to Play, Action, Multiplayer, Sandbox
Release : 8 Jul 2014
Metascore: Not Available
Price: Free

You can download the game free from Steam

http://store.steampowered.com/app/301520