Khan Academy is a free online learning platform offering a wide range of educational content and resources, including interactive courses, practice exercises, videos and articles. It covers topics in mathematics, science, engineering, computing, and the humanities. The Khan Academy app for Android and iOS provides access to all of the platform's content and features, allowing users to learn on the go or at their own pace. Khan Academy also offers personalized learning tools, such as a dashboard, practice recommendations, and progress tracking, to help users stay on track and reach their learning goals. The app also includes a library of content for educators to use in their classrooms. Khan Academy’s mission is to provide a free, world-class education for anyone, anywhere.
It's free, simple with an extensive catalog.