Abundant Music - Generate royalty free music with a simple but very powerful procedural music creator
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
AIVA - The AI composing emotional soundtrack music
music21 - Music21 is a Python-based toolkit for computer-aided musicology.
WolframTones - Listen to what I just found in the WolframTones music universe
Harmony Assistant - Harmony Assistant is an unbeatable software for computer-assisted music composition and editing.