Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
AMPLI.FI - Live online music community. Twitch for tunes.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Bandlab - Capture, nurture, and collaborate on song ideas in the cloud
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
Soundstripe for Twitch - Free music for Twitch streamers