At the end he write the setup cost him $20, but the display alone sells for $50 (from the amazon link he provided). I'm assuming he had a bunch of the components already, but that's not really a fair cost comparison.
There seem to be some 15 inch all-in-ones but these days if what you want is a small form factor the answer is surely a laptop. Even if you're just going to keep it on the same desk forever that's what you'd get if you want 15 inch or smaller.
I wonder why he didn't use a RP2350, it costs practically same as the older RP2040. That way it could have 450 kB or so system RAM, enough to play around with some old productivity software.
The old Macs really were the perfect form factor for a compact desktop computer—you saw them in every bedroom in every 1990s sitcom.
Are there any good options these days that are smaller than a 24" all-in-one?
I think he is 3d printing a 1/2 size classic Mac chassis for the oi2040 rig
Edit, this isn't the one I read but looks like the idea is older than I thought as someone was doing it in 2015:
https://www.randomorbit.co.uk/?p=904
https://arstechnica.com/apple/2025/06/new-filament-lets-you-...
I dont want to belittle the authors work, but I would call this "building custom hardware for a pico-Mac project."