I use Syncthing to keep various folders synced between my desktop, laptop, phone and tablet.
Most of the folders are just between laptop and desktop (writing, art, etc...) and my phone's camera folder is set up to share to the desktop so it syncs as soon as I take a picture.
While it's not an exact replacement in that it does all files, we have been happy with our recent switch. They have a desktop and mobile apps that handle all the syncing.
Its nice, but Memories app as part of Nextcloud is better and Nextcloud completes the rest of the Google suite (Drive, Calendar, Notes, Reader, Podcasts, Hangouts)
If you're going to put in the time, Nextcloud has more value.