What are the most commonly used (or most popular) configuration management software packages available?
The four most popular configuration management software packages are: Chef, Puppet, Ansible and Salt. They are reviewed in this article and in this video. Bottom line: Chef and Puppet have been around much longer and thus are more established but some would argue that Salt and Ansible offer more elegant solutions. A more exhaustive list of open-source configuration management software in available on Wikipedia. I chose Ansible because it's powerful, easy to learn/use, requires no daemons, no agents, no dedicated management host, no PKI, no extra databases, and no clients or open ports because it uses SSH.