Math Overflow, where intimidatingly clever mathematicians ask and answer research-relevant questions, has just been upgraded to version 2.0 of the Stack Exchange software which has powered the site since it opened in 2009.
This is news because Math Overflow has merged with the commercial Stack Exchange network, losing its (semi-)independent status. There was a tiny bit of controversy when the merge was announced last year, but the majority of users seem to be happy with the move.
Math Overflow remains separate from Mathematics Stack Exchange (yes, the naming convention is a bit confusing), which is for lower-level questions about non-research maths.
via François Dorais on Google+