Khan Academy 147 alternatives | Website
Khan Academy is not-for-profit with the goal of changing education for the better by providing a free world-class education to 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. The Khan Academy's materials and resources are available to you completely free of charge.