Duplicity is a backup program that is similar to rdiff-backup in some ways. It grew out of rdiff-backup, is also written in Python, and uses librsync for bandwidth efficiency. However, rdiff-backup's archives are meant to be as easy to view as possible, while duplicity's are as hard to view as possible---they can be encrypted with GnuPG. Also, duplicity saves data in the more conventional full+forward delta format instead of rdiff-backup's mirror+reverse deltas. Finally, rdiff-backup another copy of rdiff-backup on the remote destination, while duplicity can access remote locations with scp or ftp (other backends may be supported later).
For more information, see the duplicity page.