OP said it's one of the "coolest", not the most groundbreaking website.

Could you share these other in-browser demos that are as amazing as this one?

This one is pretty cool that i saw some time ago, not a game though, but a 3D portfolio: https://www.jessezhou.com/. The author even goes into how he made it: https://jesse-zhou.medium.com/jesses-ramen-case-study-77bae7....