You owe John Cage at least .99 it’s a fact. You should go buy his official Prepared Piano app right now. Do it.
From the site-
The sounds of John Cage’s Prepared Piano are now available for you to play on your portable device with this innovative app. Play meticulously sampled sounds of a piano prepared with the actual materials used by John Cage in the preparations for his Sonatas and Interludes (1946-48) as sampled under the supervision of the John Cage Trust.