The Nana project is aimed at providing a software framework for cross-platform GUI programming, there are many commponents, such as graphics user interface, threads. Nana is a free/open-source library written in C++ with OO and generic.
Nana is a C++ library, in Standard C++, that means it can work great with modern C++ features, such as lambdas, concurrency and so on, it will give you wonderful experiences on GUI programming with C++11. Using its own widgets, drawing functions abstracted from the Nana abstract GUI system, it allows for writting programs on supported OS, such as Windows/Linux(X11).
Nana is a free/open-source library, it is distributed under Boost Software License, which is a lax, permissive non-copyleft free software license. Now, Nana is trying to build an active developer community to give help in using this library.