Amazon's games, Every Word and Shuffled Row, are word games that are sort of versions of single-player speed Scrabble. Though they're more brainy than action-oriented due to the sluggish nature of E-ink screens, both have timed modes that raise the level of intensity (you use the Kindle's built-in keyboard to input words).
To add the titles to your Kindle, you simply purchase them in the Kindle Store like you would any free title and it will appear on your Kindle when you turn on the wireless and select "sync & check for items" from the menu.
Amazon opened the Kindle up to developers in January, so we expect to see more apps arrive, particularly after Amazon begins shipping new Kindles on August 27. Comments?