Brad Neuberg from Sitepen wrote an extensive tutorial about Creating Offline Web Applications with Dojo Offline.

What is Dojo Offline?

Dojo Offline is an open-source toolkit that makes it easy to create sophisticated, offline web applications. It sits on top of Google Gears, a plugin from Google that helps extend web browsers with new functionality. Dojo Offline makes working with Google Gears easier; extends it with important functionality; creates a higher-level API than Google Gears provides; and exposes developer productivity features. In particular, Dojo Offline provides the following functionality:

• An offline widget that you can easily embed in your web page with just a few lines of code, automatically providing the user with network feedback, sync messages, offline instructions, and more
• A sync framework to help you store actions done while offline and sync them with a server once back on the network
• Automatic network and application-availability detection to determine when your application is on- or off-line so that you can take appropriate action
• A slurp() method that automatically scans the page and figures out all the resources that you need offline, including images, stylesheets, scripts, etc.; this is much easier than having to manually maintain which resources should be available offline, especially during development.
• Dojo Storage, an easy to use hashtable abstraction for storing offline data for when you don’t need the heaviness of Google Gear’s SQL abstraction; under the covers Dojo Storage saves its data into Google Gears
• Dojo SQL, an easy to use SQL layer that executes SQL statements and returns them as ordinary JavaScript objects
• New ENCRYPT() and DECRYPT() SQL keywords that you can mix in when using Dojo SQL, to get transparent cryptography for columns of data. Cryptography is done on a Google Worker Pool thread, so that the browser UI is responsive.
• Integration with the rest of Dojo, such as the Dojo Event system

Dojo Offline is built to work with the 0.9 release of Dojo, and will not work with older versions of Dojo, such as 0.4. It also requires the Google Gears plugin to function; if users do not have it installed Dojo Offline will prompt users to download it.

Google announced Google Gears at Google Developer Day 2007.

Google Gears is an open source browser plugin that will enable developers to create offline web applications using JavaScript APIs. As a developer, you’ll be able to make an application with the assurance that it will work offline and online across browsers.

Google Reader is the first online application to offer “Gears-enabled offline capabilities”. After you load the Gears plugin you get a new icon at the top of your Reader window which enables offline capabilities of Google Reader.

The great news about Google Gears is that Dojo and Google are working together; Dojo Offline has been ported to use Google Gears as the base platform.

Ajaxian has interviewed Brad Neuberg from Dojo Offline, listen to the podcast.