Might want to try Riot. It uses a protocol called Matrix, which is the successor to IRC. What this means is that you're not tied to them. Also the web, desktop, and mobile clients are pretty sweet.
It may be aiming for it, and I do hope we see an open chat protocol succeed over all the Slacks and HipChats, but calling it the successor right now seems a little disingenuous!
Edit: Note this statement is based on my talking to people actually at matrix, on the dev team.