Google App Engine - Key Points

Google App Engine (GAE) is a Platform As a Service (PaaS) offering from Google
Is a fully managed serverless (no servers to provision or manage) platform for developing and hosting web/mobile applications at scale
Provides deployed applications with bundled services and APIs such as NoSQL databases, in-memory caching, task queues, task schedulers, load balancing, traffic splitting, logging, monitoring, and health checks
Is suitable for workloads that are highly variable or unpredictable like web and mobile applications
Offers free daily usage quota
Supported application runtimes - Python, Java, Node.js, PHP, Ruby, Go
Has a 60 second application timeout
Applications run in containers that are hosted on Google Compute Engine (GCE) VM instances
Offers two environments - Standard and Flexible
Each application has an instance class that determines the compute resources and pricing

Offers simpler deployment experience
Low utilization applications might be able to run at no charge (1 GB of data storage and traffic for free)
Runtimes are provided by Google and cannot be modified
Provides runtimes for specific versions of supported programming languages
Deployed applications run in a secure, sandboxed environment, using the supported runtimes
Read and write access to /tmp directory on the local disk
Does not provide SSH access to VM instances
Not suitable for applications written in languages other than the supported runtimes

Allows users to customize the runtime and even the operating system of the VMs using Dockerfiles
Instead of the sandbox, users can customize the default runtimes or provide their own runtime by supplying a custom Docker image or Dockerfile
Allows use of SSH for debugging and to deploy custom Docker containers
Allows applications to write to the local disk but are ephemeral
VM instances are restarted on a weekly basis to apply any necessary operating system and security updates