Impressionistically it's like git and rsync had a baby, oh, but it's a fileystem. That's how it feels with the lightweight snapshots (like branches/tags/commits in git) and the send/receive (like straight up rsync).

If there were a "merge" or "rebase" concept in this world, I think I'd have uses for it.

I've been using Duplicity for my off-site backup for a while now. It's almost obsoleted by btrfs send/receive. (As are most backup tools, at least from the thousand foot view.) All it needs is encryption and compression, with the filesystem already providing the deltas.