Puppet
Configuration management — Luke Kanies, 2005 (now Perforce). Define the desired end state in a Puppet DSL; agents converge each node toward it.
Client-server architecture (puppet master + puppet agent). Manifests + modules + Forge library (1500+ modules). Hiera for data/code separation. Bolt for ad-hoc task orchestration.
Lost momentum to Ansible (agentless) and Terraform (cloud IaC) after 2015. Lives on in Linux fleet management at large enterprises (telco, finance, regulated industries).