Of the nine programs I looked at, Rainlendar is a much slicker product but a tad more difficult to use. Rainlender is not only a reminder program but a very capable "iCal compatible" desktop calendar, though the calendar feature can be turned off. Used as a reminder and "to do" program, it's very feature rich with a really snazzy interface employing things like variable windows transparency, impressive mouse-over effects, hotkeys, and easy skinning. It also has the ability to synchronize events between clients, as well as Outlook appointment integration (Pro version). I liked, too, the way the tray icon shows the current date.