Zulip is a kind of annoying name, and every time I encounter it it's in the context of some open source platform hiding their community discussion forum behind a login. I'm left with a not very great impression.
FYI, for a while now you can mark any Zulip channel as public, which means the chat history for that channel does not require a login to view. See https://zulip.com/help/public-access-option for more details.
