Salt(stack) is an orchestration/configuration management tool which, together with Puppet and Ansible, is one of the most prominent representatives of this genre.
Salt is the middle between the other two tools: On the one hand, Salt allows automated configuration management by using a master-client principle, similar to Puppet.
On the other hand Salt as well as Ansible can be used without a client and via SSH. A unique selling point of Salt is the Reactor System. This allows fully automatic actions to be triggered in response to certain events, for example rebooting a system after installing updates.