Czech glass artist Michal Zahradnik> designed this all-glass steam engine, which he claims is fully operational and can run at 500rpm. Some of his other creations include a model plane and Harley-style motorcycle. All I know is the sound this thing makes is going to haunt my dreams.
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.