From Panda Systems:
PandoCalendar is a useful Mac-only program places a fully functional calendar on your desktop. The look is completely customizable. You can change the calendar font and its size, and the calendar's background color; you can center the current week (so you are always able to look back and ahead a full month at a time), display the numerical number of the weeks of the year, display the calendar with European style weeks (Monday being the first day and Sunday being the last), assign notes to any day of the year by clicking on the day in the calendar, and set alarms to remind you of time sensitive events. You can also have PandoCalendar automatically plot the days you work. Great for people who don't have a Monday-Friday work schedule.