IMGUI is still pretty impressive though. You can certainly create modal/non-modal windows, menus, custom widgets, file dialogs, fonts, drag and drop, unicode, tables without any other libraries. It's just that the approach is fundamentally different from what you see in retained-mode GUIs. (And if you need any OS-specific functionality like file dialogs, you can easily use other external libraries)
One of the few weaknesses of IMGUI is theming though. Don't expect to create one of those fancy Material-themed apps with animations, it's primarily intended for creating dry, technical tools of the likes of game engines and modelling/animation tools. It's more in the mindset of creating 'tools' rather than 'apps', and it really depends on your usecase.
