It’s a self hosted application that displays the poster art from your media library to a digital sign, tv, or anything with a web browser. It connects to Radarr, Sonarr, and Plex to get the currently playing, releasing soon (and monitored) and your Plex library items.
See the project here: https://github.com/petersem/posterr
I have a separate screen mounted to the wall that shows posters on rotation. It’s an android tablet essentially, but made for interactive store displays.