Prism is an application that lets users split web applications out of their browser and run them directly on their desktop.
Prism lets users add their favorite web apps to their desktop environment. When invoked, these applications run in their own window. They are accessible with Control-Tab, Command-Tab, and Exposé, just like desktop apps. And users can still access these same applications from any web browser when they are away from their own computers.

Prism isn’t a new platform, it’s simply the web platform integrated into the desktop experience. Web developers don’t have to target it separately, because any application that can run in a modern standards-compliant web browser can run in Prism. Prism is built on Firefox, so it supports rich internet technologies like HTML, JavaScript, CSS, and ´canvas´ and runs on Windows, Mac OS X, and Linux.