For years Rockstar Games has been developing a PSP successor to Beaterator, its 2005 web-based beat-producing application. Beaterator finally emerges in September. But you can see it in action here on a PSPgo, with music producer Timbaland at the helm.
I recently got an advance demo of Beaterator in action and will have coverage of the PSP title next week. Can't say any more or Rockstar PR will be on the hunt. Can't allow that. They're only a few blocks away.