Valve. It is currently avaliable on Windows, Xbox 360, and Playstation 3. It is also avaliable to download for Windows and Mac OS X through Steam. The game involves teleporting yourself through portals, which are shot with a portal gun. You are stuck in a jail-like room. Then GLaDOS, a robot, forces you to take part in pointless tests for the sake of it. GLaDOS eventually goes mad and tries to kill you. The game is set in the Half-Life universe.