An AppEngine Developer is responsible for designing, developing, and implementing applications on Google's App Engine platform. Their tasks include analyzing software requirements, creating scalable and reliable applications, writing clean, maintainable code, and testing and debugging applications to ensure their functionality. They also manage app versions, traffic splitting, and deployment strategies. They work closely with other developers, software engineers, and stakeholders to meet project objectives, ensuring the application is optimized for Google's cloud infrastructure. Additionally, they must stay updated with the latest App Engine and Google Cloud developments to improve efficiency and performance.