Laravel Debugbar (Integrates PHP Debug Bar)
Clockwork - php dev tools in your browser - server-side component
The DebugBundle allows greater integration of the VarDumper component in the Symfony full-stack framework.
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().
PHP errors for cool kids
Xdebug — Step Debugger and Debugging Aid for PHP
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.