Big fan of Zulip here. Admittedly, I haven't used Zulip in the context of a company. But I'm a happy user of - leanprover.zulipchat.com (~4000 messages /

Big fan of Zulip here. Admittedly, I haven't used Zulip in the context of a company. But I'm a happy user of - leanprover.zulipchat.com (~4000 messages / week) - coq.zulipchat.com (~1200 messages / week) - categorytheory.zulipchat.com (~600 messages / week) as well as the quieter - isabelle.zulipchat.com - hott.zulipchat.com For research groups, it seems to work exceedingly well. The UI is unobtrusive, and values my screen real estate. (Slack only devotes < 50% of the screen to the actual conversation. On Zulip, the list of users and threads are delegated to the margins, so that the actual messages have the center stage.) Besides that, I find that Zulip found the Goldilocks-equilibrium with its threading model. It works really well for both synchronous and asynchronous conversations, and you can easily switch back and forth between the two within one thread. I'm a big fan.