There are various cultural differences between refining rationality and mathematics, one of which I present here, not as a critique but to highlight possible difficulties in emulating MathOverflow's success.

-Mathematics is taught in schools. Everyone is at least passingly familiar with mathematics. People gain prestige and money from studying mathematics, even when it is not very productive in terms of solving life problems. (I happen to be one of these people!)

--In schools, there are simple mathematics problems and methods with correct answers. It's very easy to set up and reference sites that you reference for simple math problems, because a "right answer" will not be controversial, nor will the questions.

So, in the OP there exists the more advanced site, MathOverflow, and less advanced sites which can help people build experience to participate. Which site is LessWrong? We currently operate at a fairly high level but I have not seen many resources for budding rationalists and these are important as well.

And, what would a budding rationalist site look like? What sorts of clear and uncontroversial questions are there in basic rationality? What sorts of clear and correct answers can be provided for schoolchildren to check their work on?

Possible examples might include Fermi problems and Bayesian problems, but even these are not uncontroversial.

Many links would be appropriate, but all are present in the OP.