Genome MIDI Sequencer offers the capabilities missing in other apps, and let's them all play together at the same tempo. The primary function, as a sequencer, is well designed, with gesture navigation to move around fluidly. The MIDI output is feature rich, able to communicate not only with MIDI hardware (through CoreMIDI/Camera Connection Kit, Line6 Mobilizer Mk I & II) but also with other apps that support Virtual MIDI. There is even the ability to record MIDI from other Apps for custom sequencing later! See it in action and get an idea for how to set up your virtual MIDI routing in this tutorial.
Disclosure: I received my copy for review from White Noise Audio.