Minute minder

I have a job that requires me to remember to do things at certain times of the day. I often get distracted when I'm using my portable apps or surfing the web. It would be great if someone could write a program that runs in the background and that will pop up reminders to do events at certain times of the day using the clock and day of the week. A key can then be hit to cancel that event and to move on to the next scheduled item. There are different things that need to be done on a friday than on a monday so being able to post different reminders on different days of the weeks would be great. Making it recurring weekly would also be great. Does anyone know of any program that does this?