Mathigon provides a series of free, interactive, online courses that are designed to complement 6th grade through college level mathematics instruction. The website was founded by Philipp Legner, who studied mathematics and the University of Cambridge and mathematics education at the London School of Economics. Legner, who currently works at Google, wanted to design a website that enabled learners to examine mathematics concepts by actively engaging in problem solving. Each course explains key concepts and skills through a series of short explanations, helpful visualizations, problem sets, and quizzes. Learners receive feedback as they work their way through each course. Visitors to this website can find courses by browsing through the course library, which sorts available courses by grade level (6-9; 10-12; College, Fun and More) and by topic (Geometry; Functions and Equations; Probability and Statistics; Calculus and Mechanics; Applied Mathematics, etc.)