Take A Break sits in the background and counts down how many minutes it is until you should next have a break.
Set the interval with the slider (from 5 minutes to one hour) and carry on working. When the interval is up, a dialog will open and tell you to have a break. There are plenty of resources out there to tell you how long a break should be, and how often. I have a couple of minutes break every twenty minutes or so. And I have Caffeine on intravenous drip...