Okay, not the center, but possibly the largest general-interest forum
near the center. Can you name another Internet forum where discussions are similar to general-interest Usenet tech groups, where even internal details or confidential information about tech companies such as Microsoft [0] or Oracle [1] leaks out from time to time?
Mailing lists? Well, yes, but there are all single-topic forum.
Twitter? Probably, but it's not a forum, and it's even responsible for killing the forums.
Reddit? Those programming groups are large, but they are closer to newsfeed where you can submit links than a forum (Hacker News is also a newsfeed, but it's discussion-orientated, some people don't even read the news). Although some communities such as r/bitcoin has plenty of important history preserved here, but not a general-interest tech forum.
4chan? It has some historical significant for Internet subcultures, but probably not in general interest.
Chatrooms? Yes. Freenode is still big, Discord has a lot of communities, but they are not forums.
My conclusion about Hacker News being the center was after a long depression that the social media has killed large forums where long opinions are elaborated. But Hacker News is still kicking around, like it was 1995.
[0] https://news.ycombinator.com/item?id=5689391 (original comment deleted, reposted here: http://blog.zorinaq.com/i-contribute-to-the-windows-kernel-w...)
[1] https://news.ycombinator.com/item?id=18442941