Since hard drive space is relatively cheap these days, and if you have a server running 24/7, you can consider the following file sync software to create one/two/n-way sync.
Syncrify - uses "rsync" to copy data. Useful if file versioning is not required(only in paid version and is fairly expensive).
Delta copy - ditto
Allway Sync - free but only support folders available in the file system (no native http/ftp support)
Good Sync - Not free for >100 files, but support file versioning and have native http/ftp support.