The “explorable” videos in this quaternion explanation are nicely done with an interesting reactive ui : https://eater.net/quaternions

Yeah I was thinking recently how to implement quaternions in a friendly way for Processing/p5.js, came up with this: https://n1ckfg.github.io/QuaternionExample/p5js/

I thought the new thing is that quaternion are better explained by geometric algebra http://www.geometricalgebra.net/quaternions.html