The name escapes me right now, but basically you had to add "friends" in the software, then dedicate a certain amount of HDD space to it. It would then back up your files to your friends' computers, and theirs to yours. Backups were encrypted so your friends wouldn't be able to see your files.
It was a super neat idea, I wish I could remember what it was called so I could see if they're still around...
Both use rsync-style deltas to only send changes, but they use a content-addressable scheme like git so renames are a small metadata change record.
Also, both offer ftp and fuse interfaces if you need to access an older backup.
I'm looking into using the incremental diff/snapshot feature of btrfs to implement a more efficient solution :P
https://en.wikipedia.org/wiki/Distributed_Replicated_Block_D...
You put the 2 TB drive somewhere else (at a relative's) and keep it updated regularly via network.
That's my set up (but with a bigger drive).
At home, I have the master copy of the data on my file server. Then I have backup #1 that is in the same location and backup #2 that is in a different location.
Both #1 and #2 get updated at night with a "timemachine-like" backup system based on rsnapshot. The network traffic goes over ssh.
Remote backup system #2 cost a UPS, a RaspberryPi and an 8 TB drive, which is about ~$250-$300 total.
The initial sync is best done locally of course, but deltas can generally easily go over network at night.
Cheap, reliable, and (relatively) easy (if you're a geek, that is).