Docker Swarm
Docker's built-in container orchestration. Launched 2014. Tried to be a Kubernetes alternative with "Docker simplicity". Lost the war to K8s 2017–2018.
docker swarm init + docker service create. Easier to learn than Kubernetes but a much smaller ecosystem. Docker EE (Enterprise) Swarm continued through 2018–2019, but Mirantis (acquired Docker Enterprise 2019) focused on K8s. Swarm Mode is still part of Docker CE but receives no active development. Lives on in tiny-cluster use cases where K8s is overkill. Modern alternative: K3s (small K8s), Nomad (Hashicorp).