Ssync is a minimalistic tool for keeping filesystems in synchronization.
The main goals in writing ssync are correctness, simplicity, speed, 
low-resource comsumption and portability. It features a number of options
to control how things are synchronized and under what conditions, as well
as useful dry-run and verbose modes.

WWW: http://alcatraz.labs.agilent.com/shaffer/ssync/