Composition and Arranging Games
Chrome Music Lab
This is a free app that uses shapes and colors instead of notes to let you visually arrange music. There are also some sound wave experiment games. This is seriously a lot of fun just to play with!
This is a free formal notation app if you want to get crunchy with your notes :) Write music and hit the play button to hear it! There is a 'pro' option, but it's not necessary to access a lot of the options.