Exactly, those are demos, and while I believe it's slightly different there's a whole culture around it that I've never been aware until recently called "demoscene"! I even have a small "Demos" section on my website with a bunch of those, not to the same level of quality though since for me it'd be a bit more like "self-contained small experiments that resulted in something cool so I put it together as a demo":
- "Zoom", hyperdrive-like effect: https://francisco.io/demo/zoom/
- "Tree generation", specify a JSON/HTML structure and it'll generate a tree: https://francisco.io/demo/tree/ (disc: it was inspired by a broken demo I saw from someone else)
- "Stereo Depth", calculate depth of a couple of stereo images using JS: https://francisco.io/demo/depth/
- "Terminal player", specify a bunch of commands in plain text and they'll be "played" like a video: https://francisco.io/demo/terminal/