Amazon has introduced plug-ins for developers using the Unity game engine to integrate in-app purchasing and GameCircle features into their Android apps for the Kindle Fire and Kindle Fire HD tablets.

The ability for Unity developers to add features such as achievements, leaderboards and sync APIs to apps they distribute through Amazon Appstore for Android with the aim of increasing user engagement and app monetisation.

 “Unity is one of the most popular tools for building mobile games. We want to make it as easy as possible for developers to quickly integrate these features and our new, free plugins make it incredibly simple to do so for anyone using Unity,” said director of Amazon Games, Mike Frazzini.

The plug-ins are free and can be downloaded from the Mobile App Distribution Portal.

Amazon introduced an in-app purchasing API earlier this year and has found that the average transaction for digital content or subscriptions generates more than twice the revenue of the average paid app transaction.