Workrave
Being plagued with an achy wrist of late. I suspect the cause is a new desk at work so my screen was not at the right height making me sit funny. So apart from resting my hand over the xmas break and getting my desk set up correctly I have also installed Workrave.
This application pops up frequent reminders to take breaks and pauses. It works very well and I reckon that everyone should have an application like this running on their computers. Maybe it should even be part of the standard operating system.