There's my project -- http://allmydata.org Tahoe . It is an open source distributed
filesystem with very nice security properties -- everything is encrypted and integrity-checked
and you can share or withhold access to any subtree of the filesystem with anyone. It uses
erasure coding so that you can choose any M between 1 and 256 and any K between 1 and M such
that the file gets spread out onto M servers, where the availability of any K of the servers
is sufficient to make the file available to you.