I love diagrams.net (formerly draw io) to design all sorts of diagrams. It’s open source (JGraph · GitHub), yet the version running on their server only allows to share the diagram with others via centralised services (such as google docs or MS onedrive). Gitlab is also a supported location to save. Gitlab itself is also centralised though, but it is half open source, and there actually even is framagit, which is a fork of gitlab! Unfortunately the diagrams net website doesn’t allow to save to framagit. However, to me it looks like it may well be possible to host a fork of the diagrams net code on a frama server and make a small modification in order to allow saving on framagit instead of gitlab (since I guess that the forked gitlab probably uses the same APIs)! I’m curious to hear your thoughts and comments on this idea.
[Btw, I’ve seen the other forum threads on diagrams net and draw io, but they don’t focus on this idea.]