It is a masterpiece! Each time I give an introduction to machine learning, I use this explorable explanation. There is a collection of a few more here: https://p.migdal.pl/interactive-machine-learning-list/
Nice list! I remember HN talking about https://students.brown.edu/seeing-theory/ when it came out but sadly it seems like this website was discomissioned. Added an entry for my data visualisation tool here: https://github.com/stared/interactive-machine-learning-list/... . Edit: found an updated link for seeing theory so I fixed it in the PR above. Feel free to cherry-pick if #24 is not relevant.
seeing-theory has a new link ig https://seeing-theory.brown.edu/