Abundant Music - Generate royalty free music with a simple but very powerful procedural music creator
Midi Studio - Full-featured, modular MIDI control surface for iOS
AIVA - The AI composing emotional soundtrack music
Navichord - Intuitive chord sequencer and MIDI controller for iOS
WolframTones - Listen to what I just found in the WolframTones music universe
IsoPad - IsoPad lets you use your Windows tablet to play electronic MIDI instruments.