Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.
Download on the App StoreAudiobus is the app that makes the rest of your setup better.
App switching
I'm not sure if this has been suggested before but:
wouldn't it be nice if all open, audiobus compatible apps would automatically be added to the Audiobus app control panel, such that we could easily switch between all apps in a project, including midi-controllers and midi-controlled sound sources that may not be continuously connected to Audiobus.