A friend of mine has written a small app with a few windows with simple controls - a glorified calculator, if you will, but with a couple of dialogs of settings. My friend is using Windows facilities, via
stdafx.h and stdafxdlg.h`. I want to get to use only standard C++ (C++14 or later) for a bit of I/O he has there, plus a GUI toolkit. It should have few requirements, no frills, no blowing up the executable size, no weird error messages if the OpenGL drivers are misconfigured - just basic desktop windows and form controls.
Must be FOSS, relatively easy to use/learn, not require and complex build tools, and not force a whole bunch of abstractions / a framework on you. So nothing like Qt or GTK.
Preference for something written using a newer C++ standard.