Firefox OS

A HTML5-based mobile OS from Mozilla (previously known as Boot to Gecko) - Firefox OS, is expected to be rolled out in 2013.

By using HTML5 and the new Mozilla-proposed standard APIs:
Web Apps for Mobile
-Firefox OS allows all features on the phone to be run with advanced HTML5, even basic messaging and call functions
-All software running on the phone will be a web app that uses HTML5 techniques and device APIs rather than platform-specific native APIs 
-Unlocks many of the current limitations of web development on mobile, allows web app to access the phone's hardware directly via JavaScript, can taking advantage of smartphone features such as gyroscopes and cameras
-As the user interface is entirely written in HTML5 browser code, a web app can be run on other browsers outside of Firefox OS
Lower Cost
-Developers will no longer need to learn and develop against platform-specific native APIs
-Users no longer need to re-purchase apps for each device from different manufacturers
-Theoretically this should bring down the cost of producing the hardware

Click to enlarge screenshot below