http://detectmobilebrowsers.com/
Simple open source regex to detect mobile browsers. Very cool, super useful. Free and open source. Yay!
http://diveintohtml5.org/storage.html
A really easy to understand intro to html5 and other stuff. Very handy, beautifully written, elegantly presented, a joy of a web page.
http://developers.whatwg.org/offline.html#offline
Very useful article on offline web apps using HTML5 cache manifests.
http://easyxdm.net/
Very handy script that might provide a way of using the browser as a proxy. Needs a little investigation to be sure.
http://browsershots.org/
BrowserShots is an open source project which allows you to see screenshots of a url in a huge number of browsers across a number of operating systems. Very useful for web site development / testing.