Khan Academy

Khan Academy offers world-class education completely free, serving 150 million users across 190 countries with a mastery-based learning system that adapts to each student. Backed by the Gates Foundation and Google, Khan Academy demonstrates that quality learning doesn’t require a paywall—proven by a 90% user satisfaction rate and a 20% improvement in test scores among regular users. It’s the only platform on this list that is fully free, making it the most accessible option for learners worldwide.