DroidRec maybe? But it seems development is no longer ongoing 🤔

The conference software used for this service is called BigBlueButton and is probably the nicest FOSS online classroom solution there is.

This will allow you to browse & contribute to projects hosted on other instances without having an account there. Imagine using the GitHub search to find a project on Gitlab, then opening an issue there without ever even leaving GitHub. The protocol is called ForgeFed.

Big +1 for Forgejo, also they are actively working on implementing Federation, i.e. in the future Forgejo servers will be able to exchange information as a federated network, just like good old Lemmy 😊 If you want to try the toolchain (Forgejo+Woodpecker CI), it’s what Codeberg.org (run by the German nonprofit organization of the same name) offers freely.