Xdebug
Xdebug is an extension for PHP to assist with debugging and development. It contains a single step debugger to use with IDEs; it upgrades PHP's var_dump() function; it adds stack traces for Notices, Warnings, Errors and Exceptions; it features functionality for recording every function call and variable assignment to disk; it contains a profiler; and it provides code coverage functionality for use with PHPUnit. マルチユーザでのデバッグもできるらしい
どんな事ができるのかの説明
IntelliJとの相互利用
設定値の説明
xdebug.soを追加するのはトラブルの種と書いてある