Keezy Drummer - Make a beat in seconds
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Sampulator - Make (and record) beats on your keyboard
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
FL Studio Mobile - Create & save multi-track music projects on a smartphone
Splice Beat Maker - Make and share beats in your browser