Theremax™ is a simple synthesizer for the iPad, inspired by the Theremin and a number of other electronic and non-electronic instruments.
This project started with on a number of ideas: first of all, what if you could see the sounds around you, and play along. Theremax™ has a frequency graph in the background; you can whistle a tune, and by touching the peaks on the screen, play the same tune. The second founding idea was using the touch surface on the iPad as a musical instrument; hardly an original idea, but we’ve worked to use the iPad in the ways it works best, rather than trying to emulate existing instruments. Finally, we wanted to create a variable precision musical instrument; if you want to see the whole range of the instrument, you can zoom all the way out. If you want to play a melody precisely, you can zoom way in.
Grab further details from – http://gordianlabs.com/theremax/
Grab Theremax now – 
Put a theremin in your pocket! Modeled after he infamous instrument that lent spooky sounds to countless classic sci-fi and horror films, Theremin-ator allows you to evoke the theremin magic by using the touch interface on your iPhone. Simply move your finger horizontally to change pitch, and vertically to control the volume. If you want a really “airy” feel, hit “options” and hit “accel”: now you can control pitch and volume by simply moving your iDevice around, touch-free.
