Music Memos by Apple - An app to capture your song ideas
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Memo.ai - Simple and elegant notes app on your Mac
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.
Better Notes - Simple notes app that ties notes together with #hashtags
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.