https://explorabl.es is a more general hub.
> especially when you can tell that the 'teacher' is also the UI designer and developer in one and there's a very high level of quality and polish. There's nothing quite like it for learning a complex subject.
Agreed. Unfortunately I think this is the inherent limitation to the explosion of such material (Bret's seminal essay [0] was almost a decade ago) - it takes an insane amount of skill, in mostly orthogonal disciplines, as well as a lot of time and effort to make it. Some tools attempt to make them a little straightforward to program, but due to the nature of it you can't really have a one size fits all solution that isn't just a general programming language + rendering engine.
And there is no "explorables industry" to fund the production of those (unlike say, textbooks), so it ends up being mostly side projects for otherwise gainfully employed developers.
It would be amazing to have eg. attempts at building an entire K-12 curriculum around explorable explanations. It's also the kind of work that probably loses in clarity and value when done by a team/committee rather than a single person dedicated to their vision.