Google Gears Beta - Enabling Offline Web Applications

   Gears provides three key features:

• A local server, to cache and serve application resources (HTML, JavaScript, images, etc.) without needing to contact a server
• A database, to store and access data from within the browser
• A worker thread pool, to make web applications more responsive by performing expensive operations in the background

Google Gears is currently an early-access developers' release. It is not yet intended for use by real users in production applications at this time.
Link: http://gears.google.com