<blockquote>Simplify pop-ups and modals using the HTML dialog element.</blockquote>

Guter Artikel über die Möglichkeiten des track-Elements

jQuery filedrop uses the HTML5 File API to allow users to drag multiple files from desktop to the browser, uploading each file to a user-specified URL.

from Microsoft

Video for Everybody is simply a chunk of HTML code that embeds a video into a website using the HTML5 <video> element, falling back to Flash automatically without the use of JavaScript or browser-sniffing.

A client-only html5 file api multiupload data uri generator, does not require a server upload, so it's super-fast!

The All-In-One Entirely-Not-Alphabetical No-Bullshit Guide to HTML5 Fallbacks

HTML5 Responsive Design: How to Determine the Real Dimensions of an Image in JavaScript

Same HTML/CSS skin and JavaScript API for HTML5 and Flash Video

HTML 5 Outliner

Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers.