Now, I don't know the first thing about music composition, but I do know that even I could pull something passable together using software like this. Jokosher is only in 0.11 release, but already it's a very usable, powerful multi-track authoring studio. From http://www.jokosher.org/:"Jokosher is a simple and powerful multi-track studio. Jokosher provides a complete application for recording, editing, mixing and exporting audio, and has been specifically designed with usability in mind. The developers behind Jokosher have re-thought audio production at every level, and created something devilishly simple to use."For an overview of what it can do, check out these screenshots.