Khan Academy

You can learn anything. For free. Spend an afternoon brushing up on statistics. Discover how the Krebs cycle works. Get a head start on next semester's geometry. Prepare for upcoming exams. Or, if you're feeling particularly adventurous, learn how fire-stick farming changes the landscape of Australia. Whether you're a student, teacher, homeschooler, principal, adult returning to the classroom after 20 years, or a friendly alien trying to get a leg up in earthly biology — Khan Academy's personalized learning library is available to you, for free. - Learn anything, for free: Thousands of interactive exercises, videos, and articles at your fingertips. Study math, science, economics, finance, grammar, history, government, politics, and much, much more...