I'm not sure I understand, because neither IRC nor Slack have the bubbles thing, that's something you'll see in Facebook Messenger or Whatsapp. Also, Riot doesn

I'm not sure I understand, because neither IRC nor Slack have the bubbles thing, that's something you'll see in Facebook Messenger or Whatsapp. Also, Riot doesn't have those bubbles, and has the list of accounts/rooms on the side. However I'm not aware of any client that opens conversations in different windows.