Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
NtEd - Music Score Notation editor.
MMA - “MMA—Musical MIDI Accompaniment” is an accompaniment generator.
Sundog Scale Studio - The MIDI chords and melodies laboratory
Harmony Assistant - Harmony Assistant is an unbeatable software for computer-assisted music composition and editing.
LilyPond - GNU LilyPond is a computer program for music engraving.