Khan Academy

Khan Academy is a nonprofit with free video lessons and practice exercises across math, science, economics, history and more, from early school levels to early college. You can work through a course in order or jump to the topic you need.

Its AI tutor, Khanmigo, is built to guide you toward an answer with questions and hints instead of handing over the solution. Availability and any cost for Khanmigo depend on where you live and how you use it, so check the current terms on the site.

Adults use Khan Academy to refresh skills they have forgotten, such as algebra before a course or statistics for work. The lessons are short, which makes it easy to fit a little practice into a day.