Symfony is a set of PHP components and a full stack framework. It's commonly used by many content management systems powering large parts of the web. Here are a few options for Symfony CMSes developers to work with:
Bolt CMS is a lightweight CMS built with the Silex Microframework. It is handy and a great alternative for developers looking for a modern PHP CMS to replace WordPress, for example.
Drupal 8 is a partial modernisation of the legacy Drupal CMS with some parts of Symfony. It's a significant release, years in the making and finally available to the public.
eZ Platform is a CMS built on the Symfony Framework. It is a total rewrite of the eZ Publish system in development from 1999. It's a completely new CMS with 15 years of heritage.
Joomla currently it uses only a single component from the Symfony project. Joomla remains a strong contender with a large number of users and extensions.
Kunstmaan CMS is a collection of Symfony2 Framework Bundles to enable developers to create web applications with CMS features.
Sulu is a new take on content management. It has been started from scratch using an existing content repository. The team is using existing components for the basics to focus on a fresh UX.
Typo3 is an established enterprise grade CMS built on PHP. In the past years they have struggled in their renewal project, but have since moved forward with Symfony components.
Graph Databases are a rising technology within the Content Management Space. Symfony CMSes are well positioned to be a part of the rise of Graph Database CMSes. In addition to Java, which many Graph Databases are built on, PHP CMSes are a valid option for Java Developers.
Enterprise content management has been ruled by Java for decades (literally). The LAMP stack (Linux, Apache, MySQL and PHP) has been lagging behind in enterprise credibility, but nowadays they've even got access to enterprise features such as BPMN and DMN. Contemporary Symfony CMSes are also alternatives to older monoliths such as WordPress or Drupal.
Data Journalism is a growing trend. Generating insightful editorial content from large masses of data is something that is on the lips in many news rooms. The tools for Data Journalism continue to be fragmented and there is a lot of room for improvement through a CMS native in "Chunky Content". Learn more about the requirements for a CMS for Data Journalism.
Headless CMSes provide developers access to content without formatting. This is not unlike RSS before it, but the contemporary methods (REST API and JSON) open up possibilities of manipulating the content as well as reading only. Read all about the basics of decoupling with a headless CMS. Also read up on how GraphQL enables freedom from CMS ecosystems.