https://math.stackexchange.com/
Because the difference is night and day. No pedantry (no pedantry on a math site! Impossible!), no assumption that askers are throwing their homework on them. In fact, my experience with mathematicians have had me question whether I choose the right career or if I should have become a mathematician. They all seem damn chill in comparison to most of us developers.
Anyway, the idea behind that site appears to be to help people learn math. Not to build the world's most polished question repository. I very much prefer the former approach.