The Mission of the Academy:
A free world-class education for anyone anywhere.Khan Academy is an organization on a mission. They are not-for-profit with the goal of changing education for the better by providing a free world-class education for anyone anywhere.All of the site's resources are available to anyone. It doesn't matter if you are a student, teacher, home-schooler, principal, adult returning to the classroom after 20 years, or a friendly alien just trying to get a leg up in earthly biology. Khan Academy's materials and resources are available to you completely free of charge.
Some other Online Reliable free sites also available.
MIT ONLINE LECTURES
AZAX ONLINE ACADEMY