This document provides an overview of CoreOS, an operating system designed for containers. It discusses CoreOS components like etcd for key-value storage and fleet for cluster management. Etcd uses the Raft consensus algorithm to maintain data replication across nodes. CoreOS also includes container runtimes like Docker and rkt, and projects like Tectonic that combine CoreOS and Kubernetes for container management at scale. Security and vulnerability scanning tools like Clair and Fast Patch are also summarized.