Ask HN: Favorite Educational Products?

I recently realized that some of my favorite purchases have been educational products. It made me curious to know - what are the all time great educational products out there I may not know about?

Some of my favorites:

Refactoring UI - A book teaching UI design fundamentals:

https://www.refactoringui.com

ThreeJS Journey: A self-paced course teaching a browser graphics library called three.js:

https://threejs-journey.com/#

Building A Second Brain: A cohort-based course teaching technologies and techniques for consuming information and using it to create:

https://www.buildingasecondbrain.com