Khan Academy fits most of your description. The number of exercises is not unlimited (because that’s an unusual requirement). It could supplement other material

Khan Academy fits most of your description. The number of exercises is not unlimited (because that’s an unusual requirement). It could supplement other material if you truly need a huge quantity of exercises. Once you’re into more advanced topics (calculus and above), mit opencourseware is probably the best quality material. Once again, the exercises are the quantity of a typical course.