MEMS devices absolutely blew my mind the first time I read about them. Thinking: "yeah, this just shouldn't exist". Like, how can you make something with moving parts out of something that normally doesn't move (polycrystalline silicon), and is very fragile at that, all the while doing it at a scale that you require similar processes as 'normal' semiconductors. You can make physical oscillators like the peeps do in this article and have surrounding circuitry to drive and measure them, levers and actuators to mount actual tools onto: probes to manipulate single cells, mirrors to control light (looking at you, DLP) and so many other things. Super interesting!