Hi, I'm a professional (applied) mathematician and a website like that for mathematics is what I always dreamt of making ;) Even tried to apply to YC once with the idea but didn't really get very far with it. The need to provide a paycheck for my family unfortunately makes it quite hard to find enough free time to proceed with the plan but maybe if there are enough people here who are interested, we can do it together?

If interested, drop me a message at jerry at millionintegrals com.

I'm sure I read an article once, maybe about Andrew Wiles, where they said something like "there is no map of mathematics, you can trace the routes from point A to point B, but you'll never get a feel for the territory"...