Website: http://www.tritonemusic.com/
Paid iPhone app: https://itunes.apple.com/us/app/rhythm-in-reach/id308463505?mt=8&uo=4&at=10l6SU
Free Android Tablet app: https://play.google.com/store/apps/details?id=com.chromatik
Website: https://www.chromatik.com/
Free Android Phone app: https://play.google.com/store/apps/details?id=com.chromatik
Free iPad app: https://itunes.apple.com/us/app/music-theory-with-audio/id438110068?mt=8&uo=4&at=10l6SU
Free iPhone app: https://itunes.apple.com/us/app/music-theory-with-audio/id438110068?mt=8&uo=4&at=10l6SU
Website: https://www.smartmusic.com/
Free iPad app: https://itunes.apple.com/us/app/id1114202174?mt=8&at=10l6SU