I've long been a fan of VSCode LiveShare. Happy to report that LiveShare works already in the beta of GitHub Codespaces (shown for user1 - lynnlangit - below).

You can see that you can share in read-only, or read-write. You can share the code, a terminal window and/or include a chat window (shown fur user2 - llangit - below).

LiveShare, combined with ability to code in a browser is a game-changer for collaboration and education.