WOAH. I just found the hidden side pane that organizes all conversations by date, the most recent changes at the top. You click on it and it shows you the whole thread. Then you click on 'new pane' and it opens just that thread in a new window!!
Well done, gentlemen. Well done.
One amusing anecdote. We very recently rolled out two bits of functionality: auto-collapsing long threads, and defaulting to replying to your own thread you started. Many of the people who jumped in and started spamming today didn't realize they were confined to their own collapsed threads. :)
I don't think HN-like multi-level threading would work very well with chat - you expect chat messages to be chronological.
Flowdock ( https://www.flowdock.com/ ) a Slack competitor, we use it at our company.
I have a hard time going back to IRC and Slack because it is so difficult when two or three conversations goes on at the same time in busy rooms. Flowdock only lets you go one conversation deep, though.