GTK+ Reference Manual
Windows
GtkDialog
— Create popup windows
GtkInvisible
— A widget which is not displayed
GtkMessageDialog
— A convenient message window
GtkWindow
— Toplevel which can contain other widgets
GtkWindowGroup
— Limit the effect of grabs
GtkAboutDialog
— Display information about an application
GtkAssistant
— A widget used to guide users through multi-step operations