Marathon: https://mesosphere.github.io/marathon/ Chronos: https://airbnb.github.io/chronos/
Mesos is a job scheduler for large distributed systems based on a quick read.
edit: and to the point, it is very natural to consider Mesos slaves as running inside of Docker containers (which may be based on CoreOS)
fleet doesn't aspire to do complex resource scheduling or high density bin-packing. The best way to accomplish these tasks is to use fleet to bootstrap more complex and higher-level services like Mesos, Kubernetes or Deis. fleet will make sure the components of those services are running in the cluster, even if machines die or are partitioned.
(CoreOS employee)
More info on the components: http://docs.deis.io/en/latest/understanding_deis/architectur...
The Kubernetes project has also documented a getting started guide for CoreOS: https://github.com/GoogleCloudPlatform/kubernetes/blob/maste...