The server is monitoring the roof files. When a change is detected (roof opening or closing), it sends a notification to all users in the relevant buildings, together with the latest image from the all sky camera.
The notifications can be tweaked from the Pushover app on your phone, tablet or smart watch, with useful features such as quiet hours, custom sounds, message priorities, etc.
This service is completely free (apart from the $4.99 one-time purchase for Pushover). You can unsubscribe at any time, from this page or directly from Pushover's website.