By far the single best MOOC I've ever taken is edX's Introduction to Biology taught by Eric Lander at MIT. <a href="https://www.edx.org/course/introduction-to-biology-the-secret-of-life-3" rel="nofollow">https://www.edx.org/course/introduction-to-biology-the-secre...</a><p>And it's 100% free! Great lectures and the simluated "TA sessions" and esp. online quizzes did a great job reinforcing my knowledge.<p>I have an undergrad degree in biology from a top research university from many years ago and this course was so informative, effective, and inspiring, that i considered dropping out of tech to go to grad school in biology. Truly excellent.<p>I've been working professional jobs for more than a decade. Despite my full-time jobs, I've dedicated hundreds (maybe thousands?) of hours of personal time over the last 6 years teaching myself vector calculus, linear algebra, abstract algebra, molecular biology, organic chemistry, and other nerdy topics. Mostly, I use textbooks and work on problem sets. I sometimes watch videos which can be super-helpful. But the best single course I've taken in that time is the MIT edX course.