ChordIQ - Learn notes, chords, sight reading, perfect pitch and more.
Band-in-a-Box - Band-in-a-Box is so easy to use!
muted.io - A magical collection of interactive music theory tools & visual reference pages for musicians and music producers
iReal Pro - iReal Pro – Music Book and Backing Tracks is a commercial music app developed by Technimo for Android and iOS devices.
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
ChordMill - Music play along app for all instruments and voices