Dyadin is an action puzzle game for two players. The game can be played on 2 PCs or on one.
The Goal in this game is to open up every gate, which allows both player to continue to the next level, by going simultaneously through the exit. This can get complicated because both players are in a different plane to move around.
While you try to open up every barrier and gate, there will be enemies in the later level, who'll hunt you down PAC-Man style.
So the game is pretty good, if you have a friend nearby to play with it.
Give it a try, here is the link: http://www.greatgamesexperiment.com/game/dyadin