Steve Hoefer at Grathio labs shows off his Arduino based door opener, which responds to knocks on the door bye timing the gaps between the sounds. If the gap matches the programmed knock, it unlocks. Let's never use keys again!
Know a little bit about Arduino and care to make your own? Check out his Instructables post!
Deviant Artist Midnight Angel put together an arm blade stylized after the ones used in the Assassin's Creed video game series. Using a drawer opening mechanism, a spring for a screen door, and a throwing knife, the weapon works surprisingly smoothly. The full instructions are on Angel's page, and you can see it in action below.