Facebook did kill off some forums, where the built-in ability to invite or ad-target a very specific audience to a group in Facebook could grow a FB group quickly. Also, no friction of signup and verify email, etc.

Could be - at least the communities I used to participate in seem to use Discord now.

I really dislike using Discord and I can't even figure out why (so it's probably me). I do know it's not the part where it is a chat app per se - I'm happily using Zulip, managing with Slack, and WhatsApp, Telegram and Slack all have their place. But something about the UI/UX of chatting in Discord just makes it a stream of conversations where I can barely follow what's going on.

Having said that in many contexts a forum with threads that have a clear topic are just so much more of an appropriate solution than chat apps. I don't understand why people prefer the latter (although it does explain why I prefer Zulip since it manages to be a good hybrid in how it organizes discussions).

I'm in the same camp, discord and discourse just aren't useful to me

My number one issue with most of those forum "successors" is that everything is hidden behind a registration wall.

That means that they won't be indexed by search engines, so I cannot serendipitously stumble across them during a random web search in the first place, and even if I somehow learned about them, having to sign up merely to read some stuff is annoying.

Isn't that also true for Facebook groups?

I don't really like Discord, so I don't use it, and have no feedback on it.

I used to run a SimpleMachines forum, and we actually wanted to prevent the contents from being indexed.

I agree - very easy to lose track of something in the random chat that occurs. I use Discord because there's where some discussion I'm interested in happens though - not much choice sometimes.

Was early reddit code the bunch of arc macros and this here (hn) originally? Was it basically a fork of pg code for this?

It was (is?) Python: https://github.com/reddit-archive/reddit

It was definitely lisp before it was python - they used to talk about a rewrite - one of the earliest reddits were the lisp reddits - my question is if it was Arc by Paul Graham or a seperate program in Common Lisp

Reddit was Common Lisp, not Arc (or Racket at all): https://web.archive.org/web/20060114065748/http://reddit.com...

Arc was released a few years after Reddit announced their Python rewrite anyways

Before the Python rewrite it was written on Common Lisp: https://github.com/reddit-archive/reddit1.0

It's the other way around. Reddit predates HN, and one of the reasons HN was made was to recreate early reddit culture (ref: https://web.archive.org/web/*/http://ycombinator.com/announc...).

Forums are still doing well in specialized communities. Model-specific car forums, for example. When your Lincoln Town Car starts making a "whoomp whoomp whoomp" noise, you can usually find the answer in one of these forums.

They are tremendously useful still, and they also contain a lot of esoteric domain-specific knowledge you can't find elsewhere.