A slightly reduced strength bulk encryption. In exchange for the reduced strength, you get the ability to rsync the encrypted files, so that local changes in the plaintext file will result in (relatively) local changes to the cyphertext file.
Duplicity implements a traditional backup scheme, where the initial archive contains all information (full backup) and in the future only the changed information is added. Also supports encryption!
The Allmydata "Tahoe" project is a secure, distributed, fault-tolerant storage grid, available under a free-software licence. You can store files in the grid and retrieve them with a cryptographically generated URI that securely identifies and decrypts