Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
MOTU Digital Performer - Get inspired, then refine your mix — all in a singular workflow.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
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.
FL Studio Mobile - Create & save multi-track music projects on a smartphone
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).