The most interesting self-learning platform I've found is expii.com created by Poh-Shen Lo https://en.wikipedia.org/wiki/Po-Shen_Loh It feeds you exercises and judging by your answers determines if you need more practice or not using an Elo rating system https://v1.expii.com/grandmaster though I get the argument of having students pay for certs ergo they actually complete the courses, this other method seems to me to…
I did a few calculus questions and noticed two aspects which I think could be improved:
1) the multiple-choice question format makes questions easier than they appear. I solved a differential-equation question by differentiating all 4 possible solutions, I would have been unable to solve it otherwise.
2) Most questions require combining several pieces of knowledge to arrive at a solution, but the Elo rating only keeps track of a score for the type of question. If you mess up a chain-rule question by misremembering the derivative of the inverse cosecant function, then you should get more questions about the inverse cosecant function rather than the chain rule, and vice versa.
That said, changing those two things would require a lot of work, so I understand why it is the way it is.