What is up with this site: https://mathoverflow.net/ ? Is it a clone or something? I wasn't paying attention and went to login, and it says that my name is unknown... What's up? I revoked access from my Google account just to be sure.
-overflow and -stackexchange are sister sites, mathoverflow specifically is research-level math-oriented, while math.stackexchange is open to questions of all levels (thanks Arturo).
That site runs on the Stack Exchange 1.0 platform.
These sites run on the Stack Exchange 2.0 platform.
For more detail and context see: