Google Compute Engine is an IAAS product that provides easy to run and flexible virtual machines with Windows and Linux as host OS. It runs on local storage, KVM, or durable storage.
Google Compute Engine integrates with other GCP technologies (e.g., BigQuery, Google Cloud Storage) to make more complex systems.
While Google Compute App is a PaaS offering under Google Cloud Platform, it provides the platform for customers to run their services or applications. It offers Infrastructure and environment both to the client, so it forms the larger umbrella with IaaS under it.
