I am not sure how familiar you are with community-driven open source software development, but the main principle is that software is created by multiple contributors on primarily a volunteer basis, in order to make the solution freely available to all.

MuseScore is an entirely free software solution. The entire source code is also freely available for anyone to download and use as they please for any non-commercial purpose.

It may be more clear to designate this a volunteer opportunity, but this would not address the fact that participation may be official, fulfilling internship requirement of various undergraduate degree programs.

As a point of further clarification, your reference above is specific to the United States, while MuseScore is organized in Europe, where most universities on the continent require a three-month unpaid internship as part of university graduation requirement.

To the original point, MuseScore is created through a community effort that is largely voluntary (similar to projects like Wikipedia or even the unpaid moderators of this forum), which is what allows the software to be made available for free.

Anyway, we'd love for you to check out MuseScore and feel free to give us your thoughts on how to make it even better. We can't really pay you, but I'm happy to buy you a beer or two if we ever cross paths (PASIC, BOA, DCI, WGI, Midwest, TMEA, NAMM, etc.).