I ended up on Piwigo. It’s pretty fully featured and allows you to set up access controls for groups. Also has client apps.

These are fully stand alone. Downloadable. So not strictly hosted I guess?

Does it need to be “hosted”?

I like both these:

yEd (https://www.yworks.com/products/yed)

Dia Diagrams (http://dia-installer.de)

I think yEd had a free version but closed source.

You might find some starting points or even projects or terms to look for in this article:

https://arstechnica.com/information-technology/2023/03/you-can-now-run-a-gpt-3-level-ai-model-on-your-laptop-phone-and-raspberry-pi/ .