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.
Zapata Racing just released the Flyboard, a water-powered jet pack available to the public. The Flyboard gets it propulsion from a jet ski idling nearby; its hose forces water to shoot out of the user's feet. Not as cool as a the real deal the public is waiting on, but I guess this is a happy medium for now.