RequireJS : RequireJS is a JavaScript file and module loader. It is optimized for in-browser use, but it can be used in other JavaScript environments, like Rhino ...
yepnope.js : A Conditional Loader For Your Polyfills!
InstantClick : InstantClick is a JavaScript library that dramatically speeds up your website, making navigation effectively instant in most cases.
SPF : A lightweight JS framework for fast navigation and page updates from YouTube
swfobject : SWFObject 2 offers two optimized Flash Player embed methods; a markup based approach and a method that relies on JavaScript & offers a JavaScript API ...
Load scripts like images. Use HTML5 and CSS3 safely. Target CSS for different screens, paths, states and browsers. Make it the only script in your HEAD. A concise solution to universal issues.