What are your favorite/most useful GitHub Gists and/or CodePen samples?

Hi all! I built GistPad (https://aka.ms/gistpad), which is a VS Code extension that allows you to create, share and talk about code samples, documentation, tutorials, and interactive playgrounds, all backed by GitHub Gists (that way you keep/manage your own data!).

In order to help new users get started quicker, and spark the imagination of what can be done with GistPad and GitHub Gists, I'm adding a new "showcase" view that will highlight some of the most interesting and useful examples across the community. The showcase will include multiple categories and will be updated every week. That way, we can drive weekly "challenges" (e.g. coolest outer space playgrounds) and continuously keep the content "fresh".

Below is what GistPad and the new showcase will look like (categories/gists are for illustration purposes).
However, before I release the showcase v1, I need your help! In order to ensure the initial showcase is as compelling/diverse as possible, I'd love to hear from folks about what their favorite GitHub Gists, CodePen pens, Bl.ocks, etc. are. The content/subject matter can be literally anything, as long as you find it cool. I'll then use folks votes to start the showcase, and then we can iterate from there 👍