Mudflat Software has released DropSync (http://www.mudflatsoftware.com/dropsync.html), a syncing tool for Mac OS X 10.5 or higher.  It's available on the Mac App Store in the Utilities section for US$10 until the end of August.

Dropsync is designed to make it easy to keep folders in sync between computers, hard drives and remote servers. It's targeted to web development, offsite back-ups, and keeping files in sync between work and home.

DropSync is based around pairs of folder trees rather than a flat list of folder pairs. While this alternate mental model takes some getting used to, the payoff is that managing folders for syncing becomes much more dynamic, according to the folks at Mudflat Software. DropSync can always infer the partner for any folder, so adding new folders to sync is just a click, or dropped folder away.

DropSync is also one of the few syncing applications that makes accessing remote computers via ssh a first class citizen, says Mudflat Software. Users can enter their log-in details and will instantly be able to browse and select folders on a remote server for syncing.  It also integrates with the Mac OS X Keychain, so passwords are stored securely and there's no need to set up public/private keypairs.

Although casual users need never look beyond the main window, DropSync is also designed with power users in mind. It is fully AppleScriptable so you can integrate it into existing workflows.  A fully featured trial is available for download from the Mudflat Software website.