Django Music Publisher - OSS
Django Music Publisher is open source (free software) solution for original music publishers (as in not for administrators or sub-publishers). It started as a pet project, a proof of concept for CWR Developer Toolset. Since version 19.1, it is no longer using this API, delivering complete functionality in the open source code.
The official documentation is on ReadTheDocs: https://django-music-publisher.readthedocs.io. It includes a user manual.
The following articles are more about underlying motives and views, including the argumentation for using open source.