[Phil Lelyveld comment: Combine this metal welder/rebar printer with the concrete-squirting building 3D printers and you've got the possibility of some pretty interesting structures.]
The ‘anti-gravity’ MX3C-Metal 3D printer from the Joris Laarman Lab is able to print lines of metal in mid-air, enabling it to create complex metal shapes with irregular surfaces.
Developed by the same company that gave us the outer space-friendly MATAERIAL, the MX3C-Metal can print lines of copper, stainless steel, aluminum or bronze. Described as a combination of a 3D printer and a welding machine, the printer extrudes the molten metal through a robotic arm, which can form the metal lines in mid-air without the need for extra support structures.