The rules are quite simple. There are two types of squares - red and green. When you "take off" your own square from the playing field you get points (the same number you see on the square), when you "take off" the square of your opponent you loose points (the same number you see on the square). The red player can move only horizontally, while the green player can move only vertically. If you choose arcade mode, you will see blue squares with the question marks. Those are surprise-surprise squares and you do not know whether you will get or loose points until you touch them. The game stops when you run out of moves. The player who has more points wins. Simple, is not it?
But you sure will need to practice to become a champion. OpenIt features multi-user support, so if you got tired of playing with computer opponent, you can play with your friends. And since OpenIt supports LAN and TCP/IP, it does not matter if your friend is sitting next to you, in another cubicle or somewhere on the other side of the Earth. And because this game is so exciting and addictive (not to mention that it spreads like a wild fire), you will soon find out that at least three quarters of your office mates would like to challenge you.