Dropbox has open-sourced Zulip
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.