Dropbox 2.4.9 - Online synchronization tool with Finder integration; free 2 GB account. (free): "
Dropbox is an application that creates a special Finder folder that automatically syncs online and between your computers. It allows you to both backup files and keep them up-to-date between systems.
Note:You must first sign up to use Dropbox.
The Dropbox application is available for OS X, Windows, and Linux. A video on the site explains more.
Version 2.4.9: Release notes were unavailable when this listing was updated.
OS X 10.4 or later
(Via MacUpdate - Mac OS X.)