It is an appstore for Flatpaks. Flatpaks are a universal app package for Linux that runs in a sort of containerized environment. They’re very prolific in the immutable linux world.

It’s closer to Slack, but Rocket Chat is another option.

I’ve been using this image with different providers for years. I would highly recommend it.

https://hub.docker.com/r/qmcgaw/ddns-updater

This is one of the jobs of OpenLDAP.