This documentation tells you how to write packaged apps. All developers, however, should know that the new APIs for packaged apps are being released as a developer preview. This means that they are evolving daily, and anything you read now might be different in the near future. Please keep up to date with the API reference and documentation.
Note: If you've written packaged apps before, your legacy packaged apps will still work the way they always have, but they won't have access to the new APIs.
Packaged apps and extensions share a common platform. They can access many of the same APIs and they have the same manifest and permissions format. If you're familiar with the Chrome Extension docs, then the Reference docs should seem familiar. Many of the reference docs are shared; we've filtered accessibility to docs that aren't.
For Chrome packaged apps to succeed, we need and want your feedback. You can enter feedback at the chromium-apps group, file a bug at the official issue tracker, or press "Send Feedback" at the bottom of every doc page.