The new apps look and behave much like the native apps you find on Windows and OS X. They're built using web technologies, but also with Chrome-specific code that means they won't be able to run on other web browsers - they're truly Chrome apps. They can exist outside of your browser window as distinct apps, work offline, and sync across devices and operating systems. They can also access your computer's GPU, storage, camera, ports, and Bluetooth connection. Chrome Apps are, for now, only available through Chrome on Windows or Chrome OS on a Chromebook. Mac users will have to wait another six weeks before their version of Chrome will be updated.
This is very important for Chrome OS - since this means it can now have applications outside of the browser. Google's plans for Chrome OS suddenly became a whole lot clearer.