"Just works" is a relative term - I use both slack and irc at work, and it took about 2 minutes to get slack running and start using it intuitively on day one. Getting into irc was a much longer process that involved researching different clients, trying to figure out why my server credentials weren't working, and realizing that they were correct the whole time after doing a reboot, then learning how to join and discover channels, filter out noise, etc etc and I still get very little use out of it. It's just for server alerts now, mostly. Every other conversation has moved to slack.