Dishonored: Rat Assassin [Free / Free (HD)] is a game about slicing rats in half, much like its inspiration Fruit Ninja is about slicing, you know, fruit in half. Our all-seeing eye usually passes over cash-in video games like these, but this one is notable on a couple of levels. It's Elder Scrolls publisher Bethesda's first iPhone and iPad game, for one, and it's also a tie-in for Bethesda's Dishonored, which is an upcoming RPG being developed for both PC and consoles.
Across the Rat Assassin's three modes, rats fly across the screen and you're charged with whacking them as they crop up. The more rats you get, generally, the higher your score. The challenge mode adds a few wrinkles to this.
Rats are kind of a big deal in Dishonored, by the way. You can possess them and use them to help you kill things or to sneak around. This video should give you some context on this, if you're a little lost.