It is sensible to take occasional breaks while using a computer for extended periods of time, in order to prevent eyestrain, stiff neck, headaches, back aches, and RSI. Sometimes you forget to rest because you are immersed in your work!
Soft191 Rest can remind you to take such breaks.
Simply specify the amount of time you want to work between breaks, the length of the breaks, and how you want to be notified when a break is due.
The program resides the system tray, out of the way, and will remind you to take a break at the specified intervals by a popup message or window (and optional sound).