Brilliant

Brilliant is a learning app for math, science and computer science, built by learning experts with roots at MIT and Harvard. Millions of people around the world learn on it — from curious adults who finally want to understand how things work, to parents who want to help their kids, to people preparing for a career change or just stretching their brains.

It works simply: instead of long videos and lectures, you get short interactive lessons where you literally get your hands on the concept. You drag graphs, build circuits, solve concrete problems step by step and instantly see whether you're getting it right. The app tracks what you already know and where you're stuck, and adjusts your pace and difficulty accordingly.