(based on Zooko's description)
Tahoe-LAFS is a Free and Open cloud storage system. Tahoe-LAFS is an application, like BitTorrent, that you can use to download files. Unlike BitTorrent, you can also use it to upload files.
Create a bitTorrent-like sharing network.
Here are much more details in the thread where I came up with that
I can think of two good deployment scenarios for Tahoe-LAFS on FreedomBox:
Deployment scenario 1: Friend-Grid
Me and my friends -- two or ten or twenty of them -- share our hard drives (e.g. USB attached hard drives dangling from ?FreedomBoxes). When you upload with Tahoe-LAFS, the file gets encrypted and then spread out over multiple of those hard drives. By default the files are not visible to any of your friends, but you can always share a URL to a specific file or directory with specific friends, which enables them to decrypt that file or directory.
This is a well-trodden path. There are always improvements that are needed, of course, around usability, but this can definitely work. Lots of people use Tahoe-LAFS like this nowadays.
Deployment scenario 2: Global-Grid
Still, it could be fun to try it. FreedomBox could possibly come with both styles -- some fraction of hard drive space could be allocated for the experimental global grid, plus a different slice of the hard drive could be configurable for the use of your specific friends.
At least one user runs Tahoe LAFS on a consumer NAS, so that's an empirical data point is that the package is not a resource monster.
The ?DreamPlug comes with a 2GB microSD card. It may require a 1 TB hard drive to the USB port.