Simply Piano - Fast and fun way to learn piano
ChordIQ - Learn notes, chords, sight reading, perfect pitch and more.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
7Pad Scales and chords - Music instrument and assistant for playing scales and chords.
Yousician - Learn to play music at home, at your own pace
Scales-Chords - Free online music tools featuring a searchable chord database and chord charts.