Slack has raised our charges by $195k per year

Since you're a nonprofit that teaches coding, it could be a great time to consider self-hosting a FOSS chat tool.

Suggestions: Campfire [0] or Zulip [1].

Also, if the data in chat is being held hostage, the org might be using chat wrong. Right tool for right purpose. If starting over, perhaps consider if it would make sense to put that documentation or whatever it is that will get "lost" from Slack into a wiki or repo or other appropriate tool?

Big empathy, though. It must be pretty crushing. But that is why serious geeks have long been for FOSS.

  [0] https://once.com/campfire (recently became FOSS) 
  [1] https://zulip.com

I'm in Hack Club, the team is moving all of us to self-hosted Mattermost. It is unfortunate that we have to re-code so many things though.

I've never used Mattermost before today. After checking out their site, I can see they are also a for-profit company. What does Mattermost offer that Slack does not, other than a bill lower than $195K/year?

Mattermost is open-core software: you can self-host and they can't turn you off or raise the price.

What's your case for calling it open-core? The whole thing is AGPLv3, so... I'd call it FOSS with some components optionally being usable under Apache 2 terms

That's how they describe themselves: https://github.com/mattermost/mattermost

> Mattermost is an open core, self-hosted collaboration platform that offers chat, workflow automation, voice calling, screen sharing, and AI integration

Interesting. Notably, they also call themselves "open source" in the "About" of the repository. I'm not aware of any critical extensions which are closed-source. The change you've highlighted was made 4 months ago under a commit that gives no explanation: https://github.com/mattermost/mattermost/pull/31247/files , and the discussion there is private.

Notably, they do have some "source-available" code that goes into the enterprise release, at https://github.com/mattermost/mattermost/tree/master/server/...

This mainly seems to relate to metrics and fuzzy search, though it's possible more will move here in the future (it looks like this is a relatively recent development). Until recently they also had experimental support for Bleve full-text search (now seemingly deprecated), but the elasticsearch enterprise feature seems to be the replacement (otherwise they use postgres's ILIKE for built-in text search)

So, all told, Mattermost was open source, and may be moving to open core. Which means now is probably the best time to create a community-maintained fork. The team edition, and almost all features, are currently still open source.