AppSafari: Quell means to stop, put an end to, or to calm. Slide the raindrop in four directions to collect pearls but be careful of traps, endless loops, and spikes. This app by Fallen Tree Games requires iOS 3.1.3 or later for the iPhone, iPod Touch, and the iPad. For the most part, Quell creates a calm and peaceful atmosphere but can be frustrating when you’re stuck on a puzzle. This is a simple, trial and error puzzle game that anyone can play.