WordPress
The Content Management System in Brief:
CMS Original Developer: Matt Mullenweg
Operation System: Cross-platform
Main Use: CMS & Blog software
License: GNU General Public License
Developers' Description:
WordPress is publishing software with a focus on ease of use, speed and a great user experience. WordPress is blessed with an active community, which is the heart of open source software.
WordPress is a powerful personal publishing platform, and it comes with a great set of features designed to make your experience as a publisher on the Internet as easy, pleasant and appealing as possible. We are proud to offer you a freely distributed, standards-compliant, fast, light and free personal publishing platform, with sensible default settings and features, and an extremely customizable core.
Vox Populi (taken from Wikipedia):
WordPress is a blog publishing system written in PHP and backed by a MySQL database. WordPress is the official successor of b2\cafelog and has a thriving user and developer community.