If you are a C++ user you might want to check out QtCreator. It makes it as easy to create GUIs as Visual Basic did back in the day, and it's free (both as in price and freedom).
Thanks. I used to be a C++ user when there were no better languages for rapid GUI application development around (C++Builder/Delphi were the best). I've switched to C# with WinForms many years ago. Now I'm going to try Qt5 with Python (just because there is no WinForms designer for Linux, nevertheless Qt Creator doesn't feel as intuitive as C++Builder, VisualBasic and WinForms designer did though I believe it can do the job) but I'm certainly interested in the web GUI world as writing a single app that is going to run on every computer (smartphones included) seamlessly via a web browser feels extremely appealing.