Wow, check this out: a 256-byte demo for the #Commodore64, which plays a cool song. To give you an idea of how tiny this program is, the music (and visuals!) is the contents of this message itself is 256 bytes long! (I got this idea from a YouTube comment)
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Explainer: https://linusakesson.net/scene/a-mind-is-born/
It was for a 4KiB C64 demo contest! One of the insane things about it is that it actually starts out as a BASIC program, and transitions into assembly. All in 256 bytes
And the explainer is about 21,915 bytes (not including images)! 256 is ~1.2% of that.
(That was in 256 bytes too :] )