AirVox is somewhat like a Thermin, Alesis AirSynth or Roland D-beam for iOS. There are 49 presets to play with that take you through the different scales and available hand motions. $2.99 in the App Store (link).
“AirVox is a unique and precise musical instrument controlled without touch — only using hand gestures and motions. Interact with AirVox via the front facing camera. Our real-time computer vision technology “sees” your hands’ movements and turns it into musical notes and tones. YOU are the instrument! No previous musical experience is required to control Airvox. Its ease-of-use and many built-in features make music creation instant, and more importantly, fun! But AirVox is also a precision instrument. You can perform with the expression and phrasing usually heard in traditional instruments.” – yonac.com
For more info: yonac.com