Building a website has never been easier. Gone -- mostly -- are the days of having to hand-code HTML and PHP scripts in order to get a slick, fully functional website, thanks to the capabilities of content management systems that do most or all of the heavy lifting for site creators.
There are boatloads of content management systems (CMSs) for serious site creators, but the most common for websites today are three open-source tools: Joomla, Drupal and WordPress. Actually, to call them "tools" is an understatement -- these are full-fledged platforms, with tens of thousands of add-on tools created by very active developer communities.
These applications have a lot of similarities. For example, all three are written in the PHP programming language, all three are licensed under the free GNU General Public License (GPL), and all three depend on the MySQL database to hold and manage the actual content within a website.