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).