Captain Chords - Write chord progressions in your favorite DAW
Midi Studio - Full-featured, modular MIDI control surface for iOS
RapidComposer - MusicDevelopments RapidComposer: Music Prototyping and Automated Composition Software
Navichord - Intuitive chord sequencer and MIDI controller for iOS
Cthulhu - VST MIDI-FX plugin for harmonic inspiration
IsoPad - IsoPad lets you use your Windows tablet to play electronic MIDI instruments.