Duplicity is a band-width efficient backup utility capable of providing encrypted, digitally signed, versioned, remote backups in a space efficient manner.
Duplicity creates an initial archive that is a full backup. All subsequent backups are incremental and only save the difference between the latest (full or incremental) backup. A full backup and corresponding series of incremental backups can be recovered to any point in time covered by the incremental backups. If an incremental backup is missing from the backup chain then any subsequent incremental backup file cannot be recovered.
Duplicity is released under the terms of the GNU General Public License (GPL), and as such is free software.