Intelligent Email Software
When I write my email, I'm sometimes REALLY absent-minded. One of the worst mistakes I sometimes make is sending mails to the wrong people. This problem could be solved by an intelligent email client that does some basic checking and then outputs an appropriate error message (e.g. "Are you sure you want to be so rude to your GRANDMOTHER?" - "Do you really want to send this business letter to yourself?" etc. etc.)
With 20-30% of the internet population ignoring unpleasant emails, I would also need a "Be a pain in the neck"-Button. The conventional method (pushing the "Forward" button and then copying&pasting the original email address by hand) gets boring after some time.
Reward: Free copy of the software.