Looking for a chat app with specific requirements

[unmagical@lemmy.ml]

I work with a mutual aid group that currently handles communications with Signal. This is acceptable from a security and privacy perspective, but severely lacking from a discoverability and reference perspective.

I'm looking for a text chat (it's okay if it also supports voice and or video, but we don't really need that) that is kinda similar to Slack or Discord regarding rooms, but that can be self hosted (obviously). Our general workflow is to allow new volunteers to join our "General chat" and then either be invited or join via open link any of the working groups they fancy. What I'm hoping for is a software that can allow us to have all those working groups in a side bar to increase engagement with some of the more behind the scenes options. I'd also love to have the ability to easily retain posts or bookmarks so we can build up quick references where we actually communicate. I haven't found a clean way to handle the general chat for 2 reasons: 1) we would like to keep it open in such a way that anyone who wants to can join, and 2) there's currently over 800 people and we regularly add more.

All told that makes the bulleted requirements for what I'm hoping for be:

• text chat software
• rooms/channels
• ability to pin posts
• ability to add arbitrary bookmarks or links
• ability to have rooms either public or private
• ability to have at least one room anyone can join without prior approval or invite
• ability to support at least 1000 users (not necessarily concurrent client connections--that can probably be about 50)
• ideally the communications can be encrypted

What I don't need but might be nice:

• voice
• video
• file share
• polling
• reminders
• plugins

We value data ownership extremely highly hence looking for self hosting options over Slack or Discord. It's okay if the general chat exists in a separate server so long as the main server with all the other rooms can federate with it somehow.

We do have some people with IT experience, and I am software engineer of over a decade so technical barriers in setting it up shouldn't be an issue, but account creation and use for volunteers needs to be dead simple.

If anyone knows of something like this (or even a FOSS tool we may be able to extend functionally to fit the last 1 or 2 bullet points) I would love to hear your suggestions.

Thanks so much!