Slack, Zulip, this feels like we are back in 1999, when the internet was divided by ICQ, AOL Instant Messanger, Windows Live Messanger, and Yahoo Messanger. (Instant/Live was a plus back then). And the only innovation over IRC was a backlog and buddy list. I wonder when the Trillian of Slack+Zulip will come out. I hope Trillian (which still exists) is already working on it.
Those types of fragmentation issues never went away, they just changed focus. Whether it is Slack vs. Hipchat vs. Zulip, or WhatsApp vs. iMessage vs. text vs. Hangouts... more options means more (and easier!) ways to contact friends, family, and coworkers, but also means that you have to memorize a "best way to reach me" chart for each individual person.
utter nonsense.