[incr Widgets] (or iwidgets) is an object-oriented "mega-widget" set,
 or collection of high-level user-interface components, based on the
 popular Tk toolkit and the itcl/itk OO framework. Iwidgets contains
 over 50 ready-to-use mega-widgets including calendar, canvasprintdialog,
 combobox, fileselectiondialog, hyperhelp, notebook, radiobox, spinner,
 and many more.