Band-in-a-Box - Band-in-a-Box is so easy to use!
Captain Chords - Write chord progressions in your favorite DAW
iReal Pro - iReal Pro – Music Book and Backing Tracks is a commercial music app developed by Technimo for Android and iOS devices.
RapidComposer - MusicDevelopments RapidComposer: Music Prototyping and Automated Composition Software
ChordMill - Music play along app for all instruments and voices
Cthulhu - VST MIDI-FX plugin for harmonic inspiration