[tunesmith]

Khan Academy can get you pretty far, if you like going through the remedial stuff then you can even take the quizzes to get "Mastery" in various subjects like Algebra, Trig, I think Calculus too. But I'd love something else that is more adaptive and gives you exercises and education as you go. As a hobbyist one of the hardest part is figuring out where to jump in so you're neither bored nor overwhelmed.