Gmail Offline : Released in Chrome webstore

Gmail Offline is is an HTML5 powered app at the Chrome Web Store that enabled you to read, archive and respond to the emails when you don't have an Internet connection.When Internet connection goes out, simply click on the Gmail Offline icon on the Chrome’s new tab page.So get ready to view emails, draft responses, and view documents when your flight doesn't have WiFi or the office's Internet connection goes down.

How to install ?
Gmail Offline will work only on Google chrome browser.If you don't have one get it : Download google Chrome
Sign into your Gmail account and download Gmail Offline (Click to download)
On the page click on Add to Chrome

To start Offline Gmail after installing, open a new tab in Chrome; In the new tab pane you will see a Gmail Offline Icon. 

Click on the icon, and Offline Gmail will load.

You can see a screen like below.Select Allow Offline mail and click continue

Now Gmail Offline is ready to use and you can see it like below

Download today and enjoy!