Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
FamiStudio - FamiStudio is very simple music editor for the Nintendo Entertainment System or Famicom. It is designed to be easier to use than FamiTracker, but its feature set is also much more limited.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
FL Studio Mobile - Create & save multi-track music projects on a smartphone