I dimly recall trying to figure out how to make modern(ish) conveniences, like flashlights or televisions, under D&D rules. An imaginative person (i.e., not me) could probably use the "building technology on top of a magic-based world" theme as the basis for some good stories.
Of course, there's probably some corollary of Rule 34 for fictional world-building, meaning there's already thousands of books out there with this theme. If anybody knows of some well-written ones, I'd be interested in having some new (good) fiction to read.
The one that springs most immediately to mind is "Wizard's Bane" by Rick Cook, which involves somebody making a programming language out of small spells which could be used to make more complex ones, but the book wasn't actually that good.
Much better written (and very popular) is "Harry Potter and the Methods of Rationality", which you can find here:
...Or in a variety of ebook formats from the author page.
Diane Duane's "Young Wizards" series never reveals much about the workings of its magic system, but it's made pretty clear that using magic effectively is mostly a matter of describing precisely what you want to happen, and closely akin to engineering. They're good books, and I like the idea of non-mysterious magic that you may have to debug before it works right.
I also bought a neat little 4-bit relais computer from this person (Kilian Leonhardt). It's got just enough program memory to do a multiplication algorithm in.
Yes, the video is mesmerizing. Reminds me of sticking an AM radio into the guts of a 6502 based computer in order to debug a crash to determine whether it was looping or had hit an illegal opcode (the sounds are noticeably distinct).
If you like this, check out Jon Stanley's similar but smaller Relay Computer Two[1]. The page gives a highly detailed explanation of how it all works including complete circuit and logic diagrams.
Also, the video is quite nice!