I deal with a lot of different clients on a daily basis. It is a bit of a chore to figure out how to tie together their different messaging apps in order to interact with them and be alerted of any needs or emergencies.
Most clients nowadays use either Slack, HipChat, Google Hangouts, and Skype. With Slack and HipChat being most popular in my regards. The main issue I have is that I use Linux and the Slack web interface is a resource hog and can only monitor one client at a time. Whichever one is loaded at the time. The HipChat web interface is a bit lighter but the same issue persists as with Slack.
Luckily with Slack you can enable either (or both) XMPP and IRC. With HipChat you can only enable XMPP.
For Slack you go to Admin Settings and enable both or your choice: