Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
cassini - Polyphonic Synthesizer for iPhone/iPod touch
FL Studio Mobile - Create & save multi-track music projects on a smartphone
zMors Modular - Full featured modular synthesizer for iOS
GarageBand - GarageBand is a fully equipped music creation studio for Mac