Comment by brendanr

Music Lab by Code.org is a Blockly-based experience, built for K-12 education, at https://code.org/music.

It's open source, and we wrote some technical documentation at https://github.com/code-dot-org/code-dot-org/blob/600ebafa52....

There were a bunch of interesting aspects to this project. One of my favorite things was developing the user programming model. Organizing your music using functions is very powerful.