Google has Google Gears which lets you access your Gmail account offline. However, if you are a fan of Adobe Air, then you will like Geemail, an application that lets you access Gmail on your desktop and also offline.

Its interface is very similar to what you see online and it also works faster than Google Gears and also provides a standalone program for accessing your mail. You wont have to configure any POP or IMAP settings to use it. One of its nice feature is that it allows you to reply to messages while you are offline also. Just compose the message and hit the send button. The application will send the message when it detects an internet connection. One feature that many of us would love to see in it is the ‘Search’ function which is not there presently.