Download yours from the App Store! Or see it in action. You can record any sound with your iPhone microphone, and then use the recording as a basis for your real-time granular jams.

Take a look in Wikipedia for more background on Granular Synthesis in general. Also, here is a great interview with Curtis Roads, one of the progenitors of digital granular synthesis, to whom we pay homage with our app name. Still more curious? Then we recommend the grand tome, Microsound.