Abundant Music - Generate royalty free music with a simple but very powerful procedural music creator
Meludia - Listening exercises and to sharpen your ear and music theory skills
AIVA - The AI composing emotional soundtrack music
GNU Solfege - GNU Solfege is free music education software.
WolframTones - Listen to what I just found in the WolframTones music universe
Auricula - Practice your sense of hearing and learn to identify intervals for your musical development.