Workrave

Workrave is a program that assists in the recovery and prevention of Repetitive Strain Injury (RSI). The program frequently alerts you to take micro-pauses, rest breaks and restricts you to your daily limit. Please refer to the feature comparison for a complete list of features, and how the program performs with respect to other programs on the market. The program runs on GNU/Linux and Microsoft Windows.
http://www.workrave.org/welcome/