A group of developers from beautydeigns just released a template which looks by far like an operating system.  This template has mainly been made using the Mootools library and will give your users a "desktop" environment while surfing on your website!

Works with IE6+, FF. Hasn't been tested yet with opera. 

 Features :

• Resizable and dragable windows
• Powerful Ajax
  
• Start menu which acts as "home"
  
• FF and IE6 compliant
  

More information on the author's website http://beautyindesign.com/joomlaos/index.php