From John Pavlus ... Design Your App on Paper, Animate It With Your iPhone Camera:
In the digital age, paper is anything but dead. Designers can use "paper prototypes" to experiment with UI designs fast and even (as in the case of Clear, a gestural iPhone app) reveal innovative user interactions. There’s just one hitch: How do you get your sketches to actually interact with each other like a digital app? An app called POP cleverly solves this problem with the iPhone’s camera--just snap some pics of your sketches, link them together with a few taps, and voila: instant interactive prototype. No coding required.