Ansible is an open-source configuration management, application deployment, and software provisioning tool that is used to deploy, configure, & manage servers. Due to ease of use, Ansible is one of the most popular automation tools. Learn to install it on Ubuntu here.
It uses YAML, which is easy to learn & does not require you to learn a complicated programming language like Ruby (used in Puppet & Chef).
Also, it does not require any special agent to be installed on client machines & only requires client machines to have Python and SSH installed, both of which are usually available on systems.