[joshvm]

Mailing lists are a good example. For example take a look at some random threads from the Linux Kernel: https://lkml.org/lkml/2025/2/20/2066

If you reply to an earlier one, the UI will handle it and show a new branch where that conversation started. I'm not a huge fan of typical mailing list web UX and usually view flat, but it's so common that I guess a lot of people like it. My opinion is probably biased from years of using/running forums, so I'm much more used to that UI.

I think newer systems like Discourse will formally track replies to you (versus a new message in the overall thread), while legacy forums like PHPBB usually just quote-reply.