This is Stockfish 3.
The big news of this version, and the reason why we have bumped version number to 3 is not due to ELO increase (that anyhow should be interesting) nor to some cool feature, but it is due to the new super awesome testing framework that Gary setup and currently runs on
This is really a new beginning for Stockfish development. A development that now is fully open and in just few weeks has already attract many people willing to test their ideas and some of their contributions have been already committed upstream: Lucas Braesch, Ryan Schmitt, Jean-Francois Romang, James Undery, Hiraoka Takuya, jhellis, Joona Kiisky (a great return!) and of course Gary Linscott.
As a technical note for people willing to compile themselves, this time you will find also the C++11 porting along the usual C++ sources. This is 100% fully functional equivalent of the std version, but on some platforms and with some compilers (like gcc 4.8) the C++11 binary may be even faster, but it’s up to you to try and to verify on your preferred platform :-)
A special thank to Jim for his always precious support in compiling the release version and to Daylen, our stockfishchess.org webmaster that silently and without fanfare has built a really beautiful site and a fully operational support service.