Drupal
(https://www.drupal.org) is an open source CMS (content management system) that specializes in customization; Drupal can deliver a complex, rich, unique digital experience. If you need custom page templates, custom content types, and data views with user-faced filters, consider Drupal. Best for medium-to-large projects.
Wordpress
(https://wordpress.org) is another open source CMS that excels in beautiful experiences using the same technology stack. Wordpress has a lower up-front cost to set up a stunning website, but with fewer easy options to customize your content structure or generate dynamic listings of data without someone who writes code. Best for small-to-medium projects.
Why choose these CMS projects?
I specialize in Drupal and Wordpress because I believe in the power of open source projects. CiviCRM also installs alongside your Drupal or Wordpress project as a module or plugin, although it brings more with it than most other modules or plugins. It leverages the technology stack, routing, etc that a CMS provides you for content management in order to deliver a more concentrated feature-set.
Both CMS options have proven track records of success with tens of thousands of installations. They build on a rich ecosystem of contributed development, helping us concentrate on customizing your site to maximize your mission impact instead of all the technical details.