Google App Engine lets app developers build scalable web and mobile back ends in any programming language on a fully managed serverless platform.

It is a cloud computing platform that allows developers to build and host web applications on Google's infrastructure. With App Engine, developers can focus on writing code without worrying about managing servers or scaling their application to handle traffic spikes.

One of the key benefits of App Engine is its scalability. Applications running on App Engine can automatically scale up or down based on traffic demands, ensuring that users always have a fast and responsive experience. This makes it ideal for web applications that experience unpredictable traffic patterns or seasonal spikes.

App Engine also offers support for multiple programming languages, including Java, Python, Node.js, and Go. Developers can choose the language they are most comfortable with and use a variety of popular frameworks and libraries to build their application.

In addition, App Engine provides a number of built-in services and APIs, such as a fully-managed NoSQL database, user authentication, and task queues. These services make it easier for developers to build sophisticated web applications without having to write all of the code from scratch.

Some common use cases for App Engine include building web applications, mobile backends, and API services. For example, a developer might use App Engine to build a web application that allows users to upload and share photos, or a mobile backend that powers a mobile app's data storage and retrieval. App Engine can also be used to build API services that provide data and functionality to other applications.

Google App Engine is a powerful and flexible platform for building and hosting web applications in the cloud. Its scalability, multi-language support, and built-in services make it a popular choice for developers looking to build sophisticated web applications without the hassle of managing their own servers.