Registered Amazon Appstore for Android users can download a new paid app for free every day. Just open the Appstore on your connected Android device, and at the top of the home screen, you will see the free app of the day.
You can also find additional deals on your computer from www.amazon.com/appstore. To find all Amazon Appstore deals, visit the Amazon Appstore home page, and look for the deals page from the navigation bar below the search box