containerd

containerd handles the low-level work of running containers - pulling images, managing storage and networking, and starting/stopping/supervising container processes - as a daemon that higher-level tools like Docker and Kubernetes build on top of rather than implementing this logic themselves. It's a CNCF graduated project and the default container runtime for most Kubernetes distributions.

containerd is a fit for platform teams building custom container infrastructure or who want to understand what's actually running containers underneath Kubernetes (also in this catalog) - most developers use it indirectly through Docker or Kubernetes rather than directly.