Google Gears is an app which lets websites to be browsed even when you are not connected.
Google Gears (BETA) is an open source browser extension that enables web applications to provide offline functionality
It also helps in bringing Google Reader functionality offline. New version of Reader is build upon Gears platform.
Google Gears saves application resources including scripts and images, offline and stores data locally in a database (relational database) and also, fine-tunes the running operations asynchronously with AJAX leveraging best of web.