Plupload is a JavaScript library licensed under GPLv2 that allows you to upload files using HTML5, Gears, Silverlight, Flash, BrowserPlus or normal forms, providing some unique features such as upload progress, image resizing and chunked uploads.
Plupload is a cross-browser multi-runtime file uploading API. Basically, a set of tools that will help you to build a reliable and visually appealing file uploader in minutes.
Historically, Plupload comes from a dark and hostile age of no html5, hence all the alternative fallbacks, like flash, silverlight and java (still in development). It is meant to provide an API, that will work anywhere and in any case, in one way or another. While having very solid fallbacks, Plupload is built with the future of HTML5 in mind.
It was created and is maintained by Moxiecode Systems AB (the developers of tinymce).