At Math Academy (https://mathacademy.com), we implement spaced repetition in combination with a knowledge graph consisting of several thousand math topics and tens of thousands of connections (and growing). We're working on a post that explains how this all works technically.
We have a Linear Algebra course (https://mathacademy.com/courses/linear-algebra) that some of you might find interesting given how often that topic shows up on HN, and we just finished our Math for Machine Learning course (https://mathacademy.com/courses/mathematics-for-machine-lear...) for anyone who might be interested in giving that a look.
I'm the founder if anyone has any questions.
Sorry about the shameless plug.;)