OpenTangent

I've made many predictions, many of which are completely off the mark. One of them however is almost guaranteed in my opinion: massive, modular, 3D printed mega-buildings. In the not too distant future we will all be living in self sufficient mega-buildings. One structure will contain city sized populations along with all the businesses, utilities and recreational facilities one would expect in a city and they will be able to be built, repaired and expanded relatively quickly and easily. These advanced construction processes will lay the foundations for a very bright future indeed.

The lower receiver is the part of a gun that actually makes it a gun, at least in the eyes of the law. It's this part that handles the ammunition intake and the trigger system and it's this part that requires a gun license to own. Apparently every other part can be bought separately by anyone without any restriction or regulation.