Stainless Games's carnage-soaked racing game Carmageddon is free as the App of the Day app. You can grab it now but get it before it's gone, because it's only free for a day.
Carmageddon is a mobile version of a game from the late 90's that originally appeared for the Mac and Windows PCs. You drive a heavily armored race car like a maniac — there are a few ways to win, like coming in first, destroying all your opponents or nailing all the pedestrians.
It's fun, albeit bloodthirsty. You can collect powerups, but avoid the cops that show up in even more heavily armored vehicles than you! Carmageddon features 28 opponents, 11 environments, a Career Mode featuring 36 levels, 30 unlockable cars, iCloud support and dozens of achievements and more.