Minecraft is slowly approaching the singularity, and people like this crafter are only speeding things along.
Redstone lets Minecraft players do some pretty cool things. It can make secret doors, for example, or simple drawbridges. Or, if you're the creative mastermind who goes by the handle ItsJustJumby, you can build a fully functional 3D printer to build your blocky structures for you. One of these things is a lot more impressive than the others.
The 3D printer uses a combination of redstone and command blocks to turn a large expanse of in-game space into a basic computer. Blocks placed in a series of chests are used as a blueprint for the 3D object, which can be anything up to 6x9x10 blocks in size. From there, it gets rather complicated, with lots of circuitry and logic going on behind the scenes before the printing happens. The video gives a basic overview of the process, but don't expect to go out and recreate the machine on your own - not without a lot of time and research, at least.
Now, before the angry comments: yes, the logic blocks skirt around some of Minecraft technology's most limiting factors. Some call them cheating. Still, you can't look at the array of over 40,000 blocks working in tandem, and say it isn't impressive. If you want a closer look at what makes the 3D printer tick, ItsJustJumby has provided the world file seen in the video for your downloading pleasure.