Special Kindle promtional deal, from 3-7 October 2013, Thursday through Monday: both of these titles are free. Penny savings for the pound foolish.
You must have to have a Kindle to play, either a Kindle device or a Kindle ap (also available free from Amazon for PC, Mac, IPhone, Android and most recent model washers and dryers).
Far better to regret what you have done than what you have not done. Enjoy anyway.