wxWidgets
in
wxWidgets is a portable, open-source C++ class library that provides APIs for a huge number of common programming tasks. It facilitates a native look and feel on each supported platform by abstracting the system APIs for areas such as UI, graphics, disk management, network access, threading, process interaction and so on.
Aside from the general excellence of the library itself, one area in which it truly shines is the quality of its documentation. Combined with the vibrant online community that develops and uses the library, this helped to make the task of porting Sidewinder to wxWidgets remarkably straightforward.