Super Hexagon developed by Terry Cavanagh is one of the most fascinating game I've ever played. I would recommend all of you to purchase this game, it worth every penny you spend. Only that the game is difficult and there's no training mode. If you intended to purchase "Super Hexagon", consider this as a trial version or a training for it.
With the same concept, all you have to do is moving the triangle clock wise or counter clock wise to avoid the arc lines crashing in to the center by touching right or left side of the screen. If you can hold on for more than 45 second, you will unlock the next speed.
Warning: this game concept is not recommended for people with motion sickness.