Napkin

Used to be, if you had an idea for the next billion dollar app, you'd just sketch it on the nearest piece of paper. Napkin lets you do the same thing, right on your phone. Designed to be quick and nimble, it offers some surprisingly advanced features, including the ability to add layout boxes, icons, text labels, and photos from your camera roll to the canvas, with a grid that keeps everything tidy. It also offers support for layers, uses simple taps and drags for control, and automatically saves your design for later when you close the app. Ideal for app developers, mobile web developers, or design nerds in general.