Guns: According to New Scientist, the first working 3-D-printed gun was printed over the summer by a member of the AR15.com gun-enthusiast forum named HaveBlue. Actually, HaveBlue printed out parts of a gun, called the lower receiver, and combined them with parts of an ordinary pistol.
House: Behrokh Khoshnevis, a professor at USC's engineering school, wants to build a 3-D printer so large, it'll spit out concrete to create a full-sized house quickly and affordably. His company Contour Crafting has been talking up the idea for nearly a decade, but its viability is still far in the future. Although Khoshnevis gave a TED talk (available on YouTube) on 3-D-printed buildings earlier this year, the closest we've gotten to seeing this in action is an animated cartoon on the company's site.