Yousician - Learn to play music at home, at your own pace
Chordsheet Maker - Create chord sheets or lead sheets quick and easily from your iPad. Add rhythms, endings, segno, codas and all what's necessary for your musicians to know what's your music about. Transcription made easy!
Simply Piano - Fast and fun way to learn piano
Tonelib JAM - Create, edit, print and listen to tablature and guitar sheet music
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Aria Maestosa - Aria Maestosa is an open-source (GPL) midi tracker/editor.