Truly C++. Very easy to use. Very easy to implement your program, which will be very compact and fast. Usable, but still growing. The best if you do not want to rely on non-(std)C++ technologies.
This nana C++ GUI Library has a really great future. I've tried it myself and was impressed with what it can accomplish. Now I think we need more examples in the help folder of the source code that actually compile. I said this because some of them either have no example, or they have it but don't compile. This can scare new-comers away, and we don't want to do that. Overall great project and bright future!
The first C++ GUI library that has and supports Standard C++ style (including C++11 features). There is no need to learn new programming styles of GUI like Wxwidgests or Qt. No need in additional interpreter like in Qt. Simply use your preferred C++ compiler and write code using Standard C++ features and style: like inheritance, virtual function, templates and much more. It's not a FaceBook but I click Like.