In the early days of the pandemic when I was at home alone and super bored, I put together a working forum system that was pretty much aimed at this problem. It had the added bonus of not using any javascript so that it would work perfectly on a default Tor browser. I used sqlite3 for ease of installation. It was mostly a self-teaching project for me to get better in Go. But it did work. I can't link to it as it has my real name plastered all over. But I've been thinking of rewriting it now that I'm a much better programmer. And this time I wouldn't have any personal details linked to it. I'd still write it in Go though. Go has great html templating that makes server-side rendering of forum-type pages dead simple. And the additions to Go's standard library over the past few years have reduced the 3rd-party dependencies considerably. I could probably pull off a rewrite with only mattn's sqlite3 module as the last remaining module pulled in.

I included a few fun ideas that I haven't seen elsewhere, like an emergency account deletion page where you just enter a TOTP code to wipe your account and posting history instantly. Admins could also do an emergency site deletion with a TOTP code as well. The philosophy is that it's aimed at people who are more concerned with security than keeping long-term records.

It also had a feature where the site sign-up could be limited to people with one-time codes. An admin page could generate a list of these codes, which the admin would give to a trusted friend. That trusted friend in turn gave out individual codes to people they trust who wanted to sign up. The idea was to make sure users and admins could credibly say they didn't know who the other was. A variation on clandestine cells.

Despite the chatroom format I do think that self-hosted, unfederated Matrix is the best option right now from the perspective of surveillance resistance.

Maybe Mattermost or Loomio? Maybe even Discourse? None of these are e2e, of course, so it's extra important to protect the server.

Freenet Messaging System (FMS) is a forum interface which uses the distributed key-value p2p storage of Freenet for publishing and hosting the content (which uses anonymous request forwarding similar to onion routing... and it's now called "Hyphanet" by its founder).

There are a few other systems that operate atop Freenet, including Freemail and some other forum systems that are very much not recommended due to illegal content.

delta.chat has some concept of e2ee mailing lists, but i'm not positive on the details. technically PGP based (though rewritten in rust), but the app doesn't expose many of the crypto details to the end user. sadly that does mean it inherits some of the weaknesses of PGP like a lack of forward secrecy. OMEMO, Signal, and Matrix all use some variant of a double-ratchet algo. I'd like to see something like this make its way into async/store-and-forward messaging, but idk if there's some reason why it hasn't.

the delta chat app is currently pretty chat-centric, but its based on email so it could be modified to fit better with long form discussions.

My org's in Loomio, it's decent for that. ~~But I think it's closed-source and paid-only.~~ nvm AGPL-3 let's gooooo

I can't believe I forgot about it, but secure scuttlebutt fits the bill here pretty well. The protocol has issues and the default clients are open to anyone by default, but the security properties of the design are pretty interesting and definitely applicable to building encrypted long form communicate nets. Bamboo Earthstar and Willow are all based on similar ideas and may also be useful. I have gotten a little use out of Briar, but being mostly phone-centric makes it hard to use the forum for actually long messages and complex discussions.

I have been working on a protocol for mobile adhoc mesh networking an general purpose coms that could fit the bill, but i'm still in the very early stages so its not really useful, but some of the research and project links at the bottom might be interesting.

Talkyard is an interesting one.