NtEd - Music Score Notation editor.
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Ensemble Online - Ensemble Online is a Free to play Action-Adventure, Role-playing, Strategy, Single and Multiplayer video game by SemiFormal Studios.
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.
Aberoth - Aberoth is an Action-Adventure, MMORPG and Fantasy-based video game by Jarbit.
music21 - Music21 is a Python-based toolkit for computer-aided musicology.