As of now, HTML5 Offline Web Applications are compatible with all major browsers but not with Internet Explorer. FireFox, Google Chrome, Mozilla, Safari and even iPhone Safari support HTML 5 offline web applications.
The main reason behind Developing offline web apps with HTML5 is to enable their use when not connected to the internet. They need to be downloaded only once for use. This provides good speed to them as all the files are now stored in the computer itself.
Developing offline web apps with HTML5 involves three different areas of HTML
* web storage
* offline caching
* web database
Things would change once a connection to the internet is established. Your browser would automatically transfer operations to local files instead of working on offline ones.