[parliament32]

I remember there being software back in the day that did exactly this.

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...

[ajb]

There's an open source one called Tahoe: https://tahoe-lafs.org/trac/tahoe-lafs There used to be a company with a more usable similar product called allmydata, but it seems to be defunct.