Today there are several open source packages available to web developers who are looking to find a platform for their own use for for developing presence for a client. All are PHP based and are configured for further development. They all also use MySQL as the database.
Linux, Apache, MySQL and PHP make up the standard LAMP stack. Such a web serving platform has been standard for many years. Data centers all support the LAMP stack as a virtual machine. Web hosts also use LAMP widely due to its easy mechanization.Today WordPress is the most widely used, if only as it has been around a very long time. Joomla and Drupal are more recent but they have seen widespread adoption as well.
This type of systems are called content management systems (CMS). In addition to the front end web site, there is a database. MySQL is the standard.
This site uses WordPress which is mature and well suited to part time development.The rivals are better suited for full time developers.
All of the CMS systems have themes which allow for a wide range of designs. It makes work for developers easier.
WordPress has the ability to save the database to XML which makes it easy to move to a new host. The rivals also have a similar capability. With larger sites the use of a dedicated web host is common.
There are also vast numbers of plug-ins and themes to customize CMS systems.