my workplace uses Hipchat, and they appear XMPP based. You can access it using your IRC client with bitlbee as a bridge (I just set this up this past weekend - I don't know why I didn't do it sooner). Not as simple as direct IRC compatibility, but something I can live with.

I imagine it's easier for them to build custom features on XMPP (since the protocol supports custom messages/actions) rather than IRC (where you'll have to build your tool around IRC's paradigm of chat-rooms and text only chat).