Khan Academy

Khan Academy is an educational non-profit with a mission to provide a free, world-class education to anyone, anywhere. You may have used our site to study for math classes or brush up on other topics. We've got a lot of content (including official SAT prep), and it's all free. We provide features for teachers and school districts to make Khan Academy a valuable supplemental resource in classrooms. We've got a 10-year-old+ code base, but the vast majority of our backend has been rewritten in Go. Our React-based frontend (and React Native-based mobile apps) talk to this backend via GraphQL. We've got a big, audacious mission and have lots more to build.