The only <script> in your <head>: Head JS is an asynchronous JavaScript loader for all of your external scripts. The scripts load in parallel, but are executed in order, so in case you have a jQuery plugin that should be executed after jQuery is executed, head.js will take care of it.
The full version of the script also contains some widely-used JavaScript that is loaded on most modern websites today. For instance a CSS modernizer (akin to modernizr), an HTML5 enabler (similar to html5shiv) and a JavaScript feature detection module are incorporated in the full script. But no worries: there is also a head.load.js version, which only contains the loader, in case you do not need all of the extra stuff.
Finally, if you have a Google account and if you, like me, believe that it would be tremendously cool to have head.js available on the Google CDN, head over to head.js on Google AJAX api’s and give it a star!