Stretchly is a helpful program that reminds you to periodically take short breaks when you are working on the computer. According to the application, "Taking regular breaks when using a computer is scientifically proven to be important for your physical and mental well-being.", and Stretchly is specifically designed to help you take these breaks. By default, it will remind you to take a short 20 second break every 10 minutes, and a longer 5 minute break every 30 minutes.
When you start Stretchly, it will run in the system tray. Clicking on the icon will open up a menu from which you can quickly check how long it will be until the next break starts, and also easily skip to the next long or mini breaks, or pause all breaks for a certain amount of time.
Also accessible from the Stretchly menu are the preferences. Here, you have a few options for the break reminders, such as whether or not to display exercise tips during breaks, or to show break reminders on all monitors. On the Schedule tab, you can change the length of mini breaks and long breaks, and set how often they'll occur. You also have the option to enable Strict Mode, which will prevent you from being able to skip any breaks, thereby forcing you to momentarily pause from your work.
You'll get a notification right before the next break is due to start. During a break, a large reminder screen will pop up with a message giving you some quick exercise and relaxation tips, along with a progress bar to indicate how long until the break is over. You also have the ability to skip any break if you wish to do so, or postpone it for another few minutes.
I think Stretchly can definitely help you stay more relaxed while working (Unless you end up finding the break reminders annoying, of course), and it performed well in my testing of it. My only real issue with Stretchly is that when installed it will take up about 180MB of hardrive space, which somehow seems far bigger than what a simple reminder application should be. Either way, though, I would still recommend giving Stretchly a try.