Khan Academy — free lessons and practice for school and adult learners

Khan Academy provides a wide range of free instructional videos, practice exercises and learning dashboards covering maths, science, computing and SAT/GCSE/A‑level style topics. It is free for learners of all ages worldwide; registration is optional but allows progress tracking, teacher/classroom features and personalised practice. Access lessons and exercises on desktop or mobile by visiting https://www.khanacademy.org and creating a free account or using the resources without logging in.