If we're going to venture out into space in a serious way, at some point we're going to need to be able to manufacture stuff. Replacement parts, tools based on needs we don't yet know, novelty Pez dispensers, etc. 3D printing is probably the best way to do this, and a major first milestone was reached on Tuesday.
The first 3D-printed object was created aboard the International Space Station yesterday, and that object was, like a high-tech ouroboros, a part for the 3D printer that made it. The object was a faceplate for the 3D printer's extruder casing, and had the Made In Space (the company that worked with NASA to build and design the 3D space printer) and NASA logos on it.
The 3D printer is an additive manufacturing printer, which uses filaments of plastic and heat to build up objects, layer by layer. The printer performed well in the microgravity environment of the ISS, though the part adhesion to the tray was stronger than expected, suggesting a possible difference in the way layers bond in microgravity.
The part will be returned to Earth at a later date for future study, and I'm sure in the meantime the crew will start sneakily printing ukuleles and silly straws and sex toys to sell on the lucrative "Space-crafted" section of Etsy.