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!
SPF : A lightweight JS framework for fast navigation and page updates from YouTube
InstantClick : InstantClick is a JavaScript library that dramatically speeds up your website, making navigation effectively instant in most cases.
hunt : Library to detect when DOM elements become visible and disappear on scroll.
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.