Bp-formdnd is a project mainly written in ..., it's free.
Progressive enhance file upload form with drag and drop if BrowserPlus is installed.
JavaScript file to progressively enhance a file upload form if Yahoo's BrowserPlus is installed. The [input type="file"] tag is replaced with a desktop drag+drop enabled [div] and file select button. Mime-type filtering is possible, so the user can be forced to choose an image only.
Note that this script is designed to only accept a single file. If you want a multiple file uploader, there's already the Upload Tool.