It depends on what you need. In the past we used GTK and wxwidgets with OpenGL but we did not like it. We started using Qt, much better(proper object oriented

It depends on what you need. In the past we used GTK and wxwidgets with OpenGL but we did not like it. We started using Qt, much better(proper object oriented by design, and cleaner design than wxwidgets) and web apps. Now we use native libs with our own multiplattform lib with bindings for each plattform: -javascript for the web. -native cocoa and windows libs, with openGL, metal and directX. -Qt for linux with OpenGL. - Native mac(iOS and cocoa) and windows.