I like also rdiff-backup which makes a mirror of a directory + reverse diffs, in case you need to move in time. http://www.nongnu.org/rdiff-backup/

Duplicity is also another tools that uses rsync algorithm to find and stores differences, but makes unfortunately incremental backups. On upside - it can store backup on anything that you can push files (FTP, S3, IMAP, ...) and it is the only rsync-related solution with encryption I could find http://duplicity.nongnu.org/

There is also a very nice full solution - BoxBackup, which unfortunately looks not very active now. It is continuous backup, with block level de-duplication, client-side encryption. Unfortunately uses its own format, where I strongly prefer to have things more standard, so you can manually fix them if something goes wrong. https://www.boxbackup.org/