Jellyfin is the completely open alternative to Plex. [Check out the demo here. ](https://demo.jellyfin.org/stable/web/index.html#!/login.html?serverid=713dc3fe952b438fa70ed35e4ef0525a)

You can download it directly to your server and here are the[ many install instructions ](https://jellyfin.org/downloads/server)depending on what kind of Linux/OS you're working with.