Besides the obvious hype and hipster “this time its different” appeal, is there any technical reason one would would prefer Slack over, say, XMPP? I looked into it only until I realized one has to pay to access chat history.
I use jabber with a friend, and frequently messages go to his other laptop, which he doesn't see until he logs onto it. Same in reverse. Similarly, history isn't unified. You can get around these problems by having your own centralised jabber chat client (like bitlbee), but that's a technician's answer, not an answer for the general public.