The VarDumper component provides mechanisms for walking through any arbitrary PHP variable. It provides a better dump() function that you can use instead of var_dump().
Clockwork - php dev tools integrated to your browser - server-side component
Xdebug — Step Debugger and Debugging Aid for PHP
Ansible Role - PHP Xdebug
Tracy: the addictive tool to ease debugging PHP code for cool developers. Friendly design, logging, profiler, advanced features like debugging AJAX calls or CLI support. You will love it.
Laravel Debugbar (Integrates PHP Debug Bar)
The Debug component provides tools to ease debugging PHP code.
Kint - a powerful and modern PHP debugging tool.
The DebugBundle allows greater integration of the VarDumper component in the Symfony full-stack framework.