Alternatives to rsync

[reko.turja at liukuma.net]

One of my users is needing rsync like functionality to transfer changed 
contents of some directories between couple of machines. As rsync 3 isn't 
open source, but GPL3 it's out of question in order to keep the system 
untainted.

The software should be relatively lightweight - no fullblown 
mirroring/backup is needed. Also hints how to achieve similar ends using 
maybe tar/ssh might do.

-Reko