Nomad
Nomad is a lightweight workload orchestrator. It offers client instance scaling as well as workload scaling.
linux windows osx open-source virt orchestration go
SaltStack
Salt is a powerful and different approach to infrastructure management, by focusing on high speed communications between large number of systems, and can perform orchestration, remote code execution and much more.
linux windows osx open-source commercial config-mgmt provisioning orchestration python
Serf
Serf is a service discovery and orchestration tool which is highly decentralized, highly available, fault tolerant, cross platform and extremely lightweight.
linux windows osx open-source orchestration go