Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Figure - Propellerhead creates world-class software products and services that inspire music makers and provide the foundation for a worldwide creative musical community.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
keezy - A colorful soundboard. Play with music.