3D Mailbox is a 3D email client that simulates operations on airports by representing each email as an airplane, folders as hangars and the junk folder as the aircraft boneyard.
Different emails are also represented by different airlines. For example emails from Italy will be delivered by Alitalia, while those from UK will be delivered by British Airways. Emails containing attachements will be delivered by FedEx, UPS or other cargo delivery companies.
Current price (on Aug 30. 2008) is $49.95.