CoreOS fleet aggregates individual machines into a single pool of resources. Instead of running a service on a specific machine, services are submitted to the fleet cluster manager, which decides where they should run. fleet handles machine failures automatically and allows for efficient resource utilization.
fleet is no longer actively developed or maintained by CoreOS. CoreOS instead recommends Kubernetes for cluster orchestration. Tectonic delivers self-driving Kubernetes for the enterprise and is available in a free tier for small clusters.