CFEngine - Configuration management system for automated configuration and maintenance of large-scale computer systems. (Source Code) GPL-3.0C
Chef - Configuration management tool using a pure-Ruby, domain-specific language (DSL) for writing system configuration "recipes". (Source Code) Apache-2.0Ruby
cloud-init - Initialization tool to automate the configuration of VMs, cloud instances, or machines on a network. (Source Code) GPL-3.0/Apache-2.0Python
Puppet - Software configuration management tool which includes its own declarative language to describe system configuration. (Source Code) Apache-2.0Ruby/C
Rudder - Scalable and dynamic configuration management system for patching, security & compliance, based on CFEngine. (Source Code) GPL-3.0Scala
Salt - Event-driven IT automation, remote task execution, and configuration management software. (Source Code) Apache-2.0Python