About Polymathy
Polymathy is a free site for learning math and science by working through exercises. Courses are ordered so that each one builds on the ones before it, which means you can trace a path from wherever you are now to whatever you eventually want to reach.
How courses fit together
Every course lists the courses it depends on. Those dependencies form a map rather than a single line, so most subjects can be reached by more than one route, and finishing one course usually opens several others. Nothing assumes knowledge you haven't had the chance to pick up somewhere earlier on the map.
How you learn here
Each course has a course book for the theory and a set of lessons for the practice. The lessons are where most of the time goes: you drag points on a graph, build expressions, and put proofs in order, at Easy, Medium, and Hard difficulty. A lesson unlocks the next once you have shown you can do it, so the order you meet things in is the order they make sense in.
The exercises and course books are written and reviewed by the people using them. If you find a mistake, you can propose a fix; if you want to write something new, you can submit it for review. Contributions that hold up become part of the course.
Where the project stands
Polymathy is in open beta. Anyone can sign up, and it is free to use, and will stay that way.
It is also early. Three courses have enough exercises to work through from start to finish. The rest of the map is drawn but not yet open, waiting on content before anyone can enroll, and more courses get added over time.
Even the three open courses are not really finished, and they are not meant to be. Exercises keep being written and revised, so a course you come back to in a year will not be the one you left. Bug reports and feedback are genuinely useful at this stage, and the fastest way to send either is the feedback page or the Discord server.