Remind! - 5.54

Remind! runs in the background, sits in the system tray, and makes it nearly impossible to forget birthdays, anniversaries, holidays, appointments, meetings, and other important events.
A reminder can also check for new email, dial phone numbers, display startup messages, synchronize system time via the Internet, send messages, and open a specified Web address. You can create recurring events and select custom sound for each notification.
In addition, you can display a stay-on-top clock, as well as have the program chime or speak the hour, half hour, and quarter hour. A Sticker feature allows you to show a sticker with a note attached to the desktop.