The Golf Handicap Calculator is a simple but accurate application that will calculate your handicap index using the USGA formula - IF - you treat it right. It is not official or sanctioned by the USGA or anybody else, but if you need a handy way to keep track of your handicap, it works just fine. Be sure to read the GHC Instructions file carefully before using the calculator. They are more complicated than actually using the calculator, but they will tell you what you need to know. The app is pretty intuitive until you have more than twenty rounds of golf to consider. Then you have to think a little to keep the thing accurate. But that is all explained in the instructions.
Obviously there are no guarantees or warranties associated with this application. You're on your own. Keep it in the short grass and enjoy.