Google App Engine
Google's original PaaS (2008) — deploy a Python/Go/Java/Node app without thinking about servers; autoscales from 0 to thousands of instances.
A pioneer of serverless. Two environments: Standard (sandboxed, fast cold start, quota-bound) and Flexible (Docker-based, less restrictive). Datastore (now Firestore) as default database, Memcache and Task Queues built in.
Lost momentum to AWS Lambda (2014) and later Cloud Run (2019, same team, more modern). Lives on in Standard Environment for existing workloads. Culturally important: defined the "12-factor app" discipline that's now standard.