Eyes Relax is a tool that reminds you about taking those breaks. It a very flexible utility, which allows you to specify two independent (short and long) work periods, the length of the breaks, break types, notification sounds and many other settings.
Eyes Relax has also the parenting features. It can enter the password-protected Parent Mode in which the user is forced to take breaks (during the break the computer is locked). This is very useful since children often forget about the real world and play video games much too long.