> No registration needed for group members This one is the most troublesome I think. Usually this is in a conferencing solutions though, so no such thing as c

> No registration needed for group members This one is the most troublesome I think. Usually this is in a conferencing solutions though, so no such thing as chat rooms, I think. Otherwise I would suppose something like XMPP with a web frontend, eg https://movim.eu/ https://movim.eu/ ejabberd supports anonymous users, though I can't say if movim or any else web-client supports that natively https://www.ejabberd.im/Anonymous-users-support/index.html https://www.ejabberd.im/Anonymous-users-support/index.html