I just got one yesterday. You can use it to trigger loops/samples in JamUp. Not sure about any other apps. I would love to see what other people have done with it outside of JampUP and iShred - I'm not sure if there's any kind of SDK. The expression pedal input was something I was happily surprised to find out about (i got it on groupon and jumped at the price without researching too much).
If you don't need to use the Stompbox, Loopy is a popular sample app that has a good interface. Again, something I would love to see hooked up to Stompbox.
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