rsync

rsync is a software application for Unix which synchronizes files and directories from one location to another while minimizing data transfer using delta encoding when appropriate.

Free Open Source Mac OS X Linux BSD Haiku Cygwin

cwrsync

cwRsync is a yet another packaging of rsync and Cygwin for Windows. You can use cwRsync for fast remote file backup and synchronization. Rsync uses the rsync algorithm which provides a very fast method for bringing remote files into sync.

Commercial Windows

lsyncd

Lsyncd watches a local directory trees event monitor interface (inotify or fsevents). It aggregates and combines events for a few seconds and then spawns one (or more) process(es) to synchronize the changes. By default this is rsync.

Free Open Source Mac OS X Windows Linux

Rsync Client

An SSH browser with an rsync transfer engine. It lets you point-and-click to rsync.

Free Mac OS X

Rsync Client - Pro Edition

An SSH browser with an rsync transfer engine. It lets you point-and-click to rsync.

Commercial