Simply Piano - Fast and fun way to learn piano
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
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.
Yousician - Learn to play music at home, at your own pace
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.