Google has enabled promotional codes on the Google Play Store, allowing app developers to generate and distribute codes to for paid apps and in-app purchases. For example, a developer could hold a contest whereby the winners could receive a paid app or certain in-app purchases for free through promotional codes.
Developers looking to take advantage of promo codes should be aware of some limitations, however. Google says that developers can only create up to 500 promo codes per quarter, and that number is split between paid app promo codes and in-app purchases together. Further, unused promo codes don't transfer between quarters, so you'll lose access to any codes left over from the previous quarter. Finally, developers can set expiration dates for promotions lasting up to one year.
Promo code support on the Google Play Store has been a highly requested feature, so it's good to see it arrive. If you're a developer and are interested in trying the feature out, you can check out Google's support site to learn how to generate promo codes for your app.