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.
Scale Heaven - Browse and play any scale/chord, chord progression.
Guitar Pro 7 - Create, play and share your tabs
muted.io - A magical collection of interactive music theory tools & visual reference pages for musicians and music producers
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.