It's hard to remember now, but once upon a time developers seemed to struggle with the idea of touchscreen gaming. It took a few early, creative games for the iPhone to really show the potential for touch, and Eliss was one of those games. It tasked players with moving planets around, mashing them together, and splitting them up, all while trying to move them to like colored portals. It's a simple concept, but when you factor in the different sizes of the portals and planets, obstacles like planet-destroying suns, and the fact that different colors can't touch, it makes for an incredibly challenging game. You'll often find yourself using as many fingers as possible just to get through a level.