I've read about the 20-20-20 rule at a number of websites now. For those that don't know the 20-20-20 rule says that "Every 20 minutes you should look at something 20 feet away for at least 20 seconds". This gives your eyes a chance to relax and if you actually get up to do this, blood flow might even return to your legs. I tend to spend too much time staring at my monitors so I thought I would implement something to help me practice the 20-20-20 rule.
I created the 20-20-20-Rule.py python script to display a small pop-up for 20 seconds every 20 minutes. If you click on the tray icon that is displays you have two options, "Quit", obvious, and "Restart", which is useful if you've been away from the computer for awhile and want to restart your 20 minutes.
You'll need the notifiaction-daemon, libnotify, and notify-python packages for this script to work. All of those can be found at the Galago project page if your distribution doesn't currently have them installed.