Google Gears

Google has launched an open source browser extension for IE and Firefox called Google Gears that enables web applications to be available offline.After you install the extension, every Gears-enabled web application will ask your permission before storing data offline.Depending on the functionality implemented in the application, Google Gears caches resource files so they're available offline, stores data in a SQLite database that has powerful search features and synchronizes data in the background.

Google Gears will enable you to read the most recent messages from Gmail while offline or to edit your documents in Google Docs even without a network connection.
Google Reader is the first Google application powered by Gears. To enter the offline mode, just click on the small arrow and all the recent feed items are downloaded to your computer. You can disconnect from the Internet or click on "work offline" in your browser and you will still be able to read your favorite feeds in Google Reader. Like in any feed reader installed on your computer. Well, almost, because Google Reader doesn't download images or other multimedia files embedded in the posts.