A Google App Engine developer designs, builds, and manages applications directly on Google's infrastructure. They work with Google Cloud Platform's suite of powerful cloud-based tools, such as Google Cloud Datastore, Google Cloud Storage, and Google Cloud SQL. They utilize App Engine's automatic scaling feature to handle applications' varying traffic levels. Developers also ensure the applications are secure, using Google's same authentication and security protocols. Additionally, they optimize application performance, manage updates, troubleshoot issues, and potentially integrate with other Google services. They work with programming languages like Python, Java, PHP, and Go, depending on the project's requirements.