Is there any open source cross platform solution that

1. encrypts stuff on the client machine 2. has a pluggable backend - i.e. can push to one (or several of) e.g. S3, equivalent commodity cloud offerings, an NFS server or an arbitrary server 3. Rotates backups 4. Depuplicates (does this conflict with clientside encryption?) 5. "Just works" (I'm happy with a config file)