I liked the old Joel on Software boards. No threads, messages posted sequentially as they are created. If you want to quote, do it manually. I feel like discussion stayed on topic or at least evolved sensibly, there were no deep tangents on pedantic matters that pushed the rest of the messages off the bottom of the page.

Edit: here's a post where Joel talks about the design of his forums.

https://www.joelonsoftware.com/2003/03/03/building-communiti...

I think there's a lot of good sense in there, if you are too young to remember, the JoS forums were the "Hacker News" of their time, a place where programmers and other people involved in software businesses had online discussions about a number of interesting things. Those forums were even simpler than HN is -- no threads, no replies to individual posts. You could read comments in linear order, and post your comment after scrolling to the bottom. That's it.