Last night the calendar widget made it into FOX 1.7.x. In the next snapshot or release you should be able to try it out. I have made a bunch of fixes since yesterday, including resizing capability so that the LAYOUT_FILL_X|Y flags will work properly on it. Also the widget can be configured to display any day as the first day of the week.
From the beginning I already implemented a week number display. The display is there, but I still have to research the algorithm a little bit more that actually determines the week number. Which day of the week is first may need to be restricted if week numbers are on.
The calendar widget also has a option to restrict the user from navigating to other months. In addition the days not currently in the displayed month can be hidden as well: