Rex is a tool, written in Perl, to ease the administration and deployment of many servers.
From the Website: With (R)?ex you can manage all your boxes from a central point through the complete process of configuration management and software deployment.
The starting point of a Rex project is its Rexfile. Rex will parse this file and executes the defined tasks on your servers. Just think of it like a Makefile but it is written in Perl.
Every Rexfile is divided into tasks. You can define a task for every logical step to install and configure your servers.
How to Install?
You only need Rex on your Workstation. No additional software is needed on your servers. You just need ssh root access to your servers. You can download Rex from rexify.org/get/. Packages are available for CentOS, Debian, Ubuntu, Fedora, Mageia and OpenSuSE. Sources are available from CPAN.
For Debian just add the Rex repository to your sources.list.d directory.
echo 'deb http://rex.linux-files.org/debian/ squeeze rex' >> /etc/apt/sources.list
After that add the GPG key to the apt keyring.
wget -O - http://rex.linux-files.org/DPKG-GPG-KEY-REXIFY-REPO | apt-key add -
And install the software. We will install rex for the core tool and rex-apache-deploy for the deployment module.
apt-get update && apt-get install rex rex-apache-deploy