Grsync is a rsync GUI (Graphical User Interface).
Rsync is the well-known and powerful command line directory and file
synchronization tool.
Grsync makes use of the GTK libraries and is released under the GPL
license, so it is opensource.
It doesn't need the gnome libraries to run, but can of course run under
gnome, kde or unity pretty fine.
It can be effectively used to synchronize local directories and it
supports remote targets as well (even though it doesn't support browsing
the remote folder).