Perl (any system supporting perl)
Enigmailer allows you to send enciphered email with an optional password hint. The recipient receives a mail message with a link to the script to facilitate deciphering. It comes in two versions, one for enciphering mail, the other also supporting multiple recipients, read receipts, attachments, and logging to allow the recipient to verify the credentials of the sender. Unlike other secure mail systems, it allows you to use your existing email address rather than forcing you to setup and use yet another one, and it does not require the recipient to have software installed on their machine (other than a browser).