UK not-for-profit Eggs for Soldiers built a life-size tank out of 5,000 cartons to help raise awareness for its upcoming March Fourth Help for Heroes Campaign.
The Hungarian Forint is used in very large quantities ($1 USD = 218 Ft) so the government recycles a few tons of it every year. After shredding it and bundling it into bricks, the currency is shipped to charitable organizations to help with their heating cost.
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.