It seems there's a market for MathematicsFault.com
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any reason https://mathoverflow.net/ can't work?
There is still a substantial void that needs filling for math questions that are more along the lines of the questions asked on this site, e.g. people asking questions anywhere along the spectrum from simple stuff to moderately complicated but not expert mathematics.
Mathoverflow is for serious/academic/research mathematics and they close down almost all questions below that threshold.