Any code I do for fun nowadays can be found on github. Of course, most of my compositions are technically software too.
A few years ago, I contributed to the open-source Gsharp musical score editor as part of Google's Summer of Code. My mentoring organization was LispNYC, and my project was to implement import/export support for MusicXML. I kept a blog chronicling my progress.
While you're here, why not read a paper I once wrote about the Muppets? Please ignore the fact that I used the word "multiple" when I clearly meant multitude in the first sentence.