Butterfly was developed to be a small tool which accepts the first day of the last menstruation cycle and returns an overview of oncoming menstruations and ovulations with infertile and fertile periods in both a calendarview and listview. The program always opens with the prognosis of the present day.
The butterfly depicted on the main window flutters on fertile days. Furthermore, the background color of the program window changes depending on menses days or chances of conceiving a boy or a girl. Extensive help is given on the statusbar just by hovering the mouse cursor over the components in the form.