Workrave 

Workrave is an application that will look after you in so many ways. Well, this is no substitute for your mom or grandmother, but it certainly helps you a lot if work forces you to carry on the same task time and again. Workrave will suggest you to take breaks at regular intervals or when you tell it to. Thus, it can help reduce the risk of suffering from repetitive stress injuries. Those can range from typing all day long to moving stuff around, shoveling, etc. I like that Workrave is an open-source project that is absolutely free and gives me the same features that most paid applications do, and more. Workrave will suggest you to take mini-breaks once in a while. It will also allow you to set a daily limit for your activities. That limit can be set in time. When you are over it, Workrave tells you to simply stop. However, sometimes you can't just stop. Workrave comes in several languages and supports a lot of platforms, ranging from Windows to Linux and Solaris. It is also available for portable platforms.