You can easily tunnel rsync over SSH. You can configure even the simplest routers to do port-forwarding, e.g. your friend's external IP on port 2222 is redirec

You can easily tunnel rsync over SSH. You can configure even the simplest routers to do port-forwarding, e.g. your friend's external IP on port 2222 is redirected to port 22 on an internal host. Rsnapshot (rsnapshot.org) is a free rsync-based backup system; it is very efficient in terms of disk space and keeps full backups, but only keeps 1 copy of each file.