Perhaps not the answer you are looking for, but if you can bridge XMPP groups to IRC (for example with Biboumi) then The Lounge (thelounge.chat) is a great Slac

Perhaps not the answer you are looking for, but if you can bridge XMPP groups to IRC (for example with Biboumi) then The Lounge (thelounge.chat) is a great Slack-like IRC client.