TouchDAW - Full-featured DAW control and general purpose MIDI control app.
Abundant Music - Generate royalty free music with a simple but very powerful procedural music creator
XotoPad - MIDI instrument controller with chords, scales, faders, and more for multi-touch Windows devices.
AIVA - The AI composing emotional soundtrack music
Midi Studio - Full-featured, modular MIDI control surface for iOS
WolframTones - Listen to what I just found in the WolframTones music universe