White Noise Audio has released Genome MIDI Sequencer (GMS) for iPad. This sequencer app makes no sounds, but controls other hardware like synthesizers and drum machines via MIDI. There are already other MIDI sequencers available for the iPad, but the special thing about GMS is that it can send and receive MIDI clock messages. So it can sync to the tempo of your hardware.
The following video by White Noise Audio introduces GMS with an Access Virus synth and a Korg Electribe drum machine:
GMS is compatible with the Line6 MIDI Mobilizer (see also the video) and any interfaces that support CoreMIDI using the Camera Connection Kit or Network MIDI. Network MIDI allows you to send events to your Mac Desktop or to other iOS devices and apps, says White Noise Audio.
GMS is now available in the App Store and costs $ 13. More information is available on the website of White Noise Audio.