Janitor is a Python script that scans your Plex Media Server at set intervals to find media that is marked as viewed. If the media is not on your "save list" it will delete it from your hard drive. As simple as that!
It's still in a very early stage of development so please keep that in mind when using it.
Instructions on how to use it can be found here: https://github.com/filipjohansson/Janitor
And for those who just wants to download the ZIP: https://github.com/filipjohansson/Janitor/archive/master.zip
Please enjoy!