AMPLI.FI - Live online music community. Twitch for tunes.
Violin by Trala - Violin by Trala is a music learning app that is designed specifically for Violin users.
Krue - Twitch for music: live streams from amazing musicians
Metronaut - An app to help you play classical music
Soundscape - Sync your music with the open source community
Piano2Notes - Piano2Notes is a web application and mobile that transcribes your piano tune into a digital word document.