Today's Free App of the Day is Siege Hero:
Originally $0.99, Siege has 67 reviews, 48 of them five stars, and only ten of them two and one star. Most of the one star reviews complain about it not opening on devices other than a Fire. It opened and ran well on my original 7" Fire.
If you've played Angry Birds, you get the basic idea: you use a catapult to hurl things at a tower to try to knock it down and kill the enemy--not pigs this time but guards with treasure.