Rdiff-backup

rdiff-backup is a GPL-licensed incremental backup utility based on (lib)rsync; it stores changes to files instead of entire duplications, reducing storage requirements. Resultant incremental data can be viewed and restored from as if it were whole file backups via FUSE-based  .

Backup
To backup again, simply run the exact same command; each increment will be individually accessible.

External resources

 * rdiff-backup tutorial at howtoforge.com
 * Unattended rdiff-backup HOWTO
 * A Debian based tutorial at linode.com