Actually that would be ONE (probably the only) use for the MyCloud things where you can enable ssh, and it comes with a usable ssh with sftp subsystem (can be used as rclone backend) and rsync binary (you can do rsync over ssh). Not that is for the MyCloud without "Home", which are much more "cloudy" things.
Otherwise of course anything else that has USB (and the network you want, wired or wifi) and runs ssh/rsync would do, including Windows if needed but most likely a Raspberry Pi or something.