I've used syncthing to keep my music, books and docs all in sync between my home server and my laptop. It does a great job. I have also used it for a few years

I've used syncthing to keep my music, books and docs all in sync between my home server and my laptop. It does a great job. I have also used it for a few years now in place of plex sync. I have plex keep certain unwatched shows optimized for mobile and I just sync that directory to my laptop and phone so I always have my unwatched shows with me. Plex sync was totally unreliable for this so I moved away from it and syncthing has never disappointed.