Earlier quoted context omitted.
Run an IRC server, configure a hubot. Yes, 'cloud'-based chat is pretty, but it's a new coat of paint over something that's been around for decades (IRC). For a company less than several thousand people, running your own singleton IRC server is about as complicated as setting up a basic 3-tier web application (i.e., a little fiddly, but not hard at all)
Compliance is an annoying issue with IRC. With Slack, Lync, or 99% of Jabber servers out there I can log every communication that takes place (outside of people using something like OTR with Jabber) - I can set up an IRC bot in every channel to log group chats, and maybe somehow disable private messages, but it's a pain in the butt to deal with IRC where compliance is a big deal (I work in healthcare). I've often toy…
[1] https://www.inspircd.org/ [2] https://github.com/joshenders/inspircd-m_chatlog