"Have a break ... have a Kit Kat!"
A lot of digital ink has been spilled about the problems of our sedentary lifestyles. Recently, I realized that sometimes I too was sitting in my chair working at the computer for 2-3 hours without getting up!
I wrote a tiny application called KitKatTimer that sits in the system tray and reminds me to take a break when I have been sitting on my bum for a long time. It is written in C# and uses Snarl to display its notifications. (For information on Snarl go here.) It knows when you are not at the computer by listening to the system idle, locked or asleep statuses. The code for KitKatTimer can be obtained here.