Here is a short list of some very good cloud based operating systems to look into.
icloud Consists of a desktop with applications and files that you run through your web browser. Because it’s running in the cloud (the internet) it can offer you impressive features such as easy sharing and rich collaboration. The icloud team is 100% committed to providing you with an exciting, reliable, and productive computing experience.
eyeOS Includes 5 powerful applications out of the box thought to be simple and easy to use: Word Processor, Calendar, Mail Client, Spreadsheets and Files Manager.
Jolicloud Brings all the benefits of cloud computing today, making your netbook the natural extension of all your other computers and mobile devices. We have mixed a super-optimized Linux* that makes the most of your netbook hardware, battery, graphics and connectivity with a cool interface that will make your life easier.
Cornelios CorneliOS is a web based OS (aka “Web OS“) that runs in your web browser. All applications and files are stored on the CorneliOS server and are accessible all the time and anywhere. CorneliOS is platform and browser independent and is available as free Open Source software under the GPL as well as under a commercial license.