The ECLiPt Mirroring Tool is a full featured FTP mirror script written in Python. It supports nice config files, many features for controlling the mirror (include, exclude of files, special watermarks for deleting files, download just the latest version of some program), as well as producing nice HTML output.
Xfiles is an interactive utility for comparing and merging one file tree with another over a network. It supports freeform work on several machines (no need to keep track of what files are changed on which machine). Xfiles can also be used as a cross-validating disk<->disk backup strategy.
rdiff-backup backs up one directory to another. The target directory ends up a copy of the source directory, but extra reverse diffs are stored in a special directory so you can still recover files lost some time ago. The idea is to combine the best features of a mirror and an incremental backup. rdiff-backup can also operate in a bandwidth- efficient manner over a pipe, like rsync. Thus you can use rdiff-backup and ssh to securely back up to a remote location, and only the differences will be transmitted. It can also handle symlinks, device files, permissions, ownership, etc., so it can be used on the entire file system.
The GNotary client is a multi-platform GUI client that allows you to select files via drag and drop from any file manager, create the secure hash sums for each file, and submit the hash list to a list of digital notary servers. Optionally, all selected files can be backed up into a zip archive. It is written in Python and requires the wxPython toolkit.
Archive is a fully drag-and-drop multi-format archiver. Drag a directory onto it to create an archive. Drag an archive onto it to extract to a directory. It can also compress and decompress streams (for example, you could drag a .gz file onto Archive and from Archive into your text editor).
duplicity is an incremental backup tool that backs up files and directories by building tar-format volumes and uploading them to a file server. By default, these volumes will be GPG encrypted, although simple gzipping is also supported. It supports local, FTP, and ssh/scp back-ends. Because it uses librsync, archives only record the parts of files that have changed since the last backup. It supports deleted files, full Unix permissions, directories, symbolic links, and fifos, but currently not hard links.