Open Source Projects in PHP
Backdrop CMS
Drupal-derived CMS for small businesses and non-profits
Open Journal Systems
Platform for managing and publishing scholarly journals
OpenSupports
Simple ticket system for customer support
Chamilo
Learning management system focused on ease of use
Chevereto
Self-hosted image and video hosting platform
ChurchCRM
Church management software for members and events
Textpattern
Elegant, standards-focused CMS for publishers
Thelia
An open-source e-commerce solution based on Symfony.
phpList
Email newsletter and marketing manager
Tiny Tiny RSS
Self-hosted RSS feed reader and aggregator
ClassicPress
WordPress 4.9 fork that keeps the classic editor
Concrete CMS
Content management system
webtrees
Online collaborative genealogy
BoxBilling
Automated billing and client management
Croogo
Free CMS built on CakePHP
CiviCRM
Open-source CRM for nonprofits
thirty bees
Fast, PrestaShop-derived e-commerce platform
SMF
Simple Machines Forum for building online communities
Clipperz
Zero-knowledge online password manager
WonderCMS
Tiny flat-file website builder
IceHrm
HR management system for employees and leave
SilverStripe
CMS and framework used by governments and non-profits
OsClass Classifieds
Free classifieds website script
RosarioSIS
Student information system for school management