Another cool one is this guy's crazy-detailed explanation of mechanical watch mechanisms with interactive diagrams using hand-written WebGL: https://ciechanow.ski/mechanical-watch/
This blog post prompted a deep dive into mechanical watch repair, further online courses and endless reading. I’m now an amateur watchmaker and spend my nights tinkering with and trying to restore vintage mechanical watches. I’ve never been nerd sniped this hard, but I love it. Fantastic hobby (albeit ridiculously expensive)
(Previously discussed on HN: https://news.ycombinator.com/item?id=31261533)