Is there a self-hosted version?
I provide a self-hosted version of Remarkbox with a yearly license fee (priced for business to business).
And is the source code available publicly?
The complete source code was not made publicly available.
That said, I'm a strong advocate of open source. Many of the libraries used to create Remarbox are open source, as well as the operating systems used to run the service. I have personally open sourced some of the custom components of Remarkbox with liberal licenses (sometimes even public domain).
At this time I'm trying to make a company out of Remarkbox so that I can eventually run it full time. To accomplish this goal I have decided against providing the complete source code in the open.
Have you looked into the Fair Source License? Seems like a good fit here. https://fair.io
The source code is available privately to Python developers, if this is you go here: https://meta.remarkbox.com/12d31ca6-680c-11eb-8f71-040140774501/calling-for-python-engineers-who-want-to-hack-on-remarkbox-code-base
If you want to hear more, I cut a video about it over my lunch break: https://youtu.be/RD0FZ-ddido