Lol, in real life those are called Nanoscale Fabricators, or a nanofab for short. They are a set of miniature production pipeline that assemble individual atoms first, passing those up stages to craft into larger and larger things until you get your output product, which has a lot of excess material to act as bindings (it needs to be fairly solid), but the unneeded bit can be made out of something that washes off easily or so though, and of course you need essentially an atom-scale blueprint of what you want to create. Modern 3d printers are essentially a larger version of those and creating the first NanoFab is the goal of quite a number of companies as once you have the first, it can craft more if you give it the raw resources needed.
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