What is "mailplane"

Mailplane is an e-mail client for Mac OS X that "wraps" the Gmail service as a site-specific browser. This gives the user a more "application-like" experience, including the ability to drag and drop files into attachments, use the OS X Address Book and Keychain, use spell checking, easily send images, and use Gmail as the outbound mailer when clicking on mailto links. It is written using Mac OS X's Cocoa and WebKit APIs. CNet awards it a five-of-five star rating.