You see, some people still think that Unity 3D is just for script kiddies and art students. Well, take that.
Arthur Lee created a game that effortlessly combines Portals and time manipulation by allowing the player to take snapshots of the game and place them somewhere else on the surfaces – where they act as snapshots not just of the view, but also of the time, therefore allowing you to go back in time.
But watch for yourself:
[Found thanks to Alex Amsel]