Amazon is running a promotion where you can earn a $5 credit, good towards the purchase of a Kindle eBook, if you download one of six select free apps from the Amazon Underground appstore. The qualifying apps are Flow Free, Simple Mahjong, Dr. Panda’s Restaurant 2, Goat Simulator, Heads Up!, and Cut the Rope: Time Travel HD. To qualify for the credit, you must not have downloaded an Amazon Underground app on an Android device before. You will receive an email informing you that you received the $5 credit, which will automatically be applied at checkout when purchasing a Kindle eBook. The promotion ends April 21st and the $5 credit you earn is valid for 10 days after you receive it.