Ocean beta - Make music with friends in your browser
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
iO-808 - Rhythm composer modeled after Roland's TR-808 drum machine.
music21 - Music21 is a Python-based toolkit for computer-aided musicology.
Cameo - Book personalized video shoutouts from your favorite people
DaCapo Editor - DaCapo Editor is a free Open Source music sheet editor which allows to easily create nice looking partitions. It is available as a web application as well as a desktop application for Windows, MacOS and Linux.