Burn Note is either completely brilliant or rather sinister. It is an e-mail service that destroys all traces of the message once sent, a la Mission Impossible:
All communication on Burn Note can be viewed only once. Burn Notes are destroyed immediately after they have been viewed by the recipient and completely extinguished from the Burn Note servers. Burn Notes are never stored in the recipient’s email and once deleted it is impossible for anyone to retrieve them.
(Via Apartment Therapy)