The psync script of MacOSX::File uses stat() attributes to do full copies onto the same directory structure stored elsewhere. Unison mostly deals with source code but seems to have a self made rsync workalike. There are several other tools that do rsync + hardlinking unchanged files.

BackupPC (http://sourceforge.net/projects/backuppc/) has a very similar concept to what I want. It is written in Perl and has a nice CGI interface. The disadvantages include using windows shares, tar, rsync as transport protocol and AFAIK checksumming only parts of a file.