I also use Plex, but it is definitely not FOSS. Jellyfin is a thing, the UI needs a LOT of work, though.
I prefer Plex mainly because it has allowed me to easily share to family without any real barriers except that the account information is controlled by a for-profit company. And to be fair to myself, I was a Plex user before it left the OSS world, back when it was a simple fork of XBMC. So I’ve been bought-in since its early versions.