What're your thoughts on MathAcademy? I heard about it here on HN several months ago, and it's been on my list of things to check out, once I finish my current two side projects.
Love it, 4 months into math for ML with a review of some earlier topics. It's actually almost entirely about practice in small chunks, which is different from many other services I've seen. (Means no sitting through longer videos / explanations) Basically it's what I would've really liked my school math to be. Each question is only a couple of minutes or so, so I really appreciate being able to do it here and there when possible, instead of having to dedicate full hours to the course. I've been following it being developed for years hoping to use it with my kid, but ended up using it myself first.