Zulipchat (https://zulipchat.com/) is a chat service that has an interactive eMail-like threading model. Content is formatted in markdown complete with code formatting and more. With its filter mechanisms, one can easily concentrate on single threads or mute threads that one is no longer interested in. Since Zulipchat is open-source, it is possible to self-host it and use a variety of authentication schemes (https://zulip.readthedocs.io/en/stable/production/authentication-methods.html).