Bvckup 2 maintains a copy of a set of folders at a nominated destination. It's most notable for its delta copy implementation that doesn't require any software running at the destination, making incremental updates especially fast. This deal will only last "a couple of days".
"Light, versatile and very capable software for professional data replication. Select a pair of folders and it will make sure that one stays an exact copy of the other. "
why not use syncthing?