Helio Workstation - Cross-platform lightweight speed-painting tool for creating music.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Guitar Pro 7 - Create, play and share your tabs
MMA - “MMA—Musical MIDI Accompaniment” is an accompaniment generator.
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
Sundog Scale Studio - The MIDI chords and melodies laboratory