Nanomachines: One of the very common forms of Applied Phlebotinium in the Empire, and the Worlds in general.  However, this being at least firm SF, they don’t cause physically implausible superpowers – and in general obey the laws of physics – do require energy sources (be it chemical or external power transmission), do need to dispose of their waste heat (a particular limitation on in-body nanomachines, given how little of it it takes to do serious damage to the host), and, by and large, require specialized operating environments to do their jobs.

And while they are incredibly useful in manufacturing, they are not the be-all and end-all; if you need a large steel casting for something, it would be ridiculously inefficient – and uneconomic – to nanofacture it rather than use a perfectly good robotic steel foundry to do the job.  Even in nanofacture, macroscopic machines with nanotech operating heads are actually much more common than swarms of independently operating assemblers.