Frontier Elite (David Braben). A vast universe, with awesome space flight mechanics (gravity, etc), great graphics/audio, all fitting on one floppy disk. It was coded in assembly:

https://en.wikipedia.org/wiki/Frontier:_Elite_II

You could do the slingshot effect in it.

For older games, I would say the original Prince of Persia. I played it on an 8088 machine, and it was pretty impressive how he made the animations sophisticated and smooth.

I've been enjoying seeing how far people have been pushing the Playdate's hardware.

'Micro Mages': https://morphcat.de/micromages/

Reminds me of this. I found their video that had a breakdown of some of what they needed to do to make a game fit on NES really fascinating!

Not entirely sure if it's fit the critera but there is usually pops up retro-themed compos for most retro platforms meaning there's natural hardware restrictions (like demos for retro platforms).

8bit like Nes (Nesjam late may/june), Gameboy(GBJam was last year, bi-annual), Atari,etc, but also for MSDOS, Amiga and more "mid-school" platforms together with semimodern like PS1.

Now, even with modern tools it's plenty of work to get impressive things working on older platforms (I had a Gameboy techdemo last time there was a compo that's due to grow ridiculously much).

+1 This needs to exist if it doesn't yet!

Maybe an issue would be people not all having the same type of hardware though? Maybe you target an emulator. (Some Fantasy Consoles sort of count here?)

I haven't looked expensively but some of the retro themed jams were missing the "spirit" I was expecting.

I did a Nokia jam a while back — monochrome, beeps — and I remember being kind of annoyed that the rules technically allowed 3D Unity games as long as they followed resolution and color palette.

(A 3D cube spinning on a TI calculator is a different matter ;)

Wolfenstein 3D would have to be on that list.

Demo parties usually have a category for games.