GoatTracker - This is a crossplatform C64 music editor.
Flowkey - The easiest way to learn piano with your iPhone or iPad
OnlineSequencer.net - OnlineSequencer.net is an online music sequencer that allows users to create beats and music tracks.
Yousician - Learn to play music at home, at your own pace
Jummbox - A modified Beepbox that have more stuff then Beepbox. It can be used just like Beepbox. The features of Jummbox is the same of Beepbox's features, but Jummbox have more stuff to offer.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.