Plupload (via). Fantastic new open source project from the team behind TinyMCE. Plupload offers a cross-browser JavaScript File uploading API that handles multiple file uploads, client-side progress meters, type filtering and even client-side image resizing and drag-and-drop from the desktop. It achieves all of this by providing backends for Flash, Silverlight, Google Gears, HTML5 and Browserplus and picking the most capable available option.