https://tableaunoir.github.io/
Tableaunoir is an open-source online collaborative blackboard solution with fridge magnets available in many languages. The word "Tableau noir" means blackboard in French. Tableaunoir differs from plenty of other collaborative boards on the Internet in these aspects. First Tableaunoir has a minimalistic graphical user interface. In particular the user may just have a completely black screen on which to write. Second, Tableaunoir respects and protect people's privacy and personal data: the system does not store any information on the server side.
Finally, with Tableaunoir the user can create intuitive explanations, interactive animations, presentations and videos. To do that, it relies on fridge/blackboard magnets like we had in childhood. These magnets can be images that the user inserts, or some portions of the blackboard that are converted into magnets. Magnets can then be moved to explain a concept.
Tableaunoir is written in HTML, CSS and Typescript. The source code is available here: source code
The documentation is available here: documentation