I have been running a Mattermost instance with a few thousand users for years now.

It really hasn’t required any maintenance at all beyond incrementing the version number.

They are starting to tighten the screws (showing admins a warning if you have over 2500 users), but it’s still looking good for a few years before I need to act on that.

Notably, Mattermost can be forked to a community edition if the team behind it does anything too user-hostile. It's a fine balance for them to keep their "team edition" nudging users to a supported edition without being so annoying that users are motivated to make that community edition.

I have other reasons to want a community edition personally, but sadly they've been successful enough thus far that there isn't enough interest from other developers to make it happen.

Forking involves:

* Fork the server (adjust your CI / build / deploy pipeline) * Run your own push notification broker * Fork the iOS client, white-label it, point it at your push server * Setup apple dev account to publish * Fork the android client, white-label it, point it at your push server * Setup google dev account to publish * Fork the frontend repo, edit to match the white-labelled apps

From one walled garden to another?

You can self-host it.

Awesome, yes I see it's open source. I was thrown off by other comments talking about "They are starting to tighten the screws"