Once upon a time, Plex started as a fork of XBMC/Kodi.

I'm still using Kodi. It still does everything I need it to do, user complaints about "dated UI" be damned.

About the only thing I wish it shipped was a built-in renamer utility to help organize the media to the naming scheme that Kodi expects in order to scrape metadata properly. Most of the leading third-party utilities for this are proprietary subscription apps, which is a huge shame when the core product is FLOSS.