We've seen before that iOS can be very powerful in terms of producing audio, but there's one big drawback, and it's that iPhones and iPads are still only designed to be used for one task at a time. If you want to do more than one task at a time (like combining beats with a synth, or processing and recording vocals), you're either out of luck, or you have to find an app that does both.
Until now, apparently. Audiobus is a brand new app for iOS that purports to have solved this problem, and will combine audio sources and actions across multiple apps somehow. That means that with Audiobus, you can play synths in one app, play drums in another, and record them all together in a third.
There are a few catches, not surprisingly. The first is that each app you use must be Audiobus compatible -- you can't just combine any app's output with any other, sadly. But there's a solid list of Audiobus apps available already, and presumably adding the compatibility in isn't too hard. Second, of course, using multiple apps at the same time can push the processor a little bit, so Audiobus recommends you use newer devices, in order to get as much power as possible.
But otherwise, this sounds like a nifty suggestion for the apps listed as compatible. Audiobus is available now for $9.99. I think this is probably the next area where Apple can grow with an official solution. Obviously, Apple has wanted to keep iOS devices targeted towards one task at a time, but if third parties start creating other ways for apps to connect, Apple may get pressured to release more and more options for sharing information across multiple apps.