Comment Syncthing (Score 1) 283
I use Syncthing. It works on Linux, macOS, Windows. There is no "master", but it is P2P so any machine can disappear and it does not matter. It can "relay" when both machines are behind firewalls. When I install a new machine I just pick what folders from syncthing I want (Music, Work, Pictures...), it pulls them, and then it is effectively another backup node. With a machine off-line I am protected against deleting my own data too.