[RobertDeNiro]

That, sounds a lot like slack

[WorldMaker]

Less like IRC and more like using a Google Docs document or Office 365 Word document collaboration for a live chat, using different paragraph formatting for threading. (Some of the Wave collaboration tech wound up in Docs.)

[jjakque]

Slack allows 2-tier conversation (and IIRC, you cannot share code snippet in 2nd tier).

Reddit and HackerNews allows n-tier conversation where you can branch a thread to heart's content.