In a step to make the Appstore an even more viable alternative to Google's Play Store, Amazon is now rolling out a new feature for developers to make more money: in-app payments.
The Play Store has had an in-app purchasing system for a while now, which allows developers to make some extra money off of their apps with things like in-game currency, subscriptions, upgrades, etc. Up to this point, developers haven't had a way to offer the same features (or capitalize on them) with the Amazon Appstore. Thanks to this new API, however, devs will be able to better market their product on the millions of devices that depend exclusively on the Appstore for their go-to app market (like the Kindle Fire, for example).
For more information on the API, as well as how you can implement the in-app payment system into your application, check out the Amazon Appstore Developers' Blog.