Amazon IoT vs AWS Greengrass: What are the differences?

Developers describe Amazon IoT as "Easily and securely connect devices to the cloud. Reliably scale to billions of devices and trillions of messages". AWS IoT is a managed cloud platform that lets connected devices easily and securely interact with cloud applications and other devices. AWS IoT can support billions of devices and trillions of messages, and can process and route those messages to AWS endpoints and to other devices reliably and securely. With AWS IoT, your applications can keep track of and communicate with all your devices, all the time, even when they aren’t connected. On the other hand, AWS Greengrass is detailed as "Local compute, messaging, data caching, and synch capabilities for connected devices". Greengrass lets you run IoT applications seamlessly across the AWS cloud and local devices using AWS Lambda and AWS IoT.

Amazon IoT and AWS Greengrass can be primarily classified as "Internet of Things Services" tools.