Google App Engine is a Platform as a Service that allows developers to build and host web applications in Google's data centers. It supports applications written in Java, Python, Go, and PHP. Developers can use App Engine's Datastore for NoSQL storage, Cloud SQL for relational databases, and Cloud Storage for file storage. Additional services like URL Fetch, Mail, and Memcache are also provided. App Engine is suitable for applications that need scalability, don't require access to local files, and can handle requests within 60 seconds.