Duplicati
Duplicati is a free backup client that securely stores encrypted, incremental, compressed backups on cloud storage services and remote file servers. It works with Amazon S3, Windows Live SkyDrive, Google Drive, Rackspace Cloud Files, WebDAV, SSH, and FTP.
Duplicati has built-in AES-256 encryption and backups can be signed using GNU Privacy Guard. Duplicati is licensed under LGPL and available for Windows and Linux (.NET 2.0+ or Mono required).