boost -- The Boost C++ Libraries
http://www.boost.org/
Boost provides free peer-reviewed portable C++ source libraries.
The emphasis is on libraries which work well with the C++ Standard
Library, in the hopes of establishing "existing practice" for extensions
and providing reference implementations so that the Boost libraries are
suitable for eventual standardization. (Some of the libraries have already
been proposed for inclusion in the C++ Standards Committee's upcoming C++
Standard Library Technical Report.)