WebOS

         Another interesting feature of cloud computing is the web-OS or web operating system, which allows users to experience a virtual operating system over the internet or any other network. Most of these web-OSes gives a virtual desktop on your browser with common software utilities. So you can store and maintain your personal data from anywhere in the world using a computer or even with a smart-phone that is connected to the internet.
>>Learn more from Wiki
 see:
HP webOS for mobile smart-phones 

Screen shots of few web-OSes:
                      
                                eyeOS

                     
                                 AstraNOS

                                 Glide

You can find many web-OSes from bellow sites.
Sign up for any of them and get new experience. (some web-OSes may not function)
links:
http://desizntech.info/2009/08/top-5-web-operating-systems/
http://mashable.com/2007/08/22/web-os/