Code.org provides free computer science activities and lessons, in particular interactive puzzles and games. It is used by millions of students globally from young to old, and some of the activities are translated in over 45 languages. It includes activities for very young children, e.g. learning about computer basics like drag and drop.
Code.org is also the creator of the annual Hour of Code campaign. It is 100% free thanks to large donations from organisations such as Microsoft, Facebook, Amazon and Google.