Dropzone is a small application that you can install on your Mac, and as the app name suggests, drag stuff onto. When you drop a file on the icon, you will get a list of options depending on what type of file you just dropped. For instance, you could drop a picture onto the icon and get an option to email, send to Flickr, or upload to an FTP server.
Different applications can "register" to work with Dropzone by using a simple API, the documentation for which can be found on the Aptonic website. The more applications that decide to work with Dropzone, the better (developers, did you hear that?). There is currently no shipping date set for this handy little Dock tool, but you can check out a teaser video on the Aptonic website, and also apply to be a part of the beta program.