Derick Rethans 于2007年7月18日正式发布了Xdebug 2，官方网址：http://xdebug.org/。

该工具用于排错确实很不错，支持堆栈跟踪、远程调试、代码分析等等，值得推荐，下面是他的原话：

It is finally here, Xdebug 2.0.0 has arrived! After about four years of work I finally found it ready to release. Have fun! After almost four years of work, Xdebug 2 is finally ready. With improved functionality and many new features it is ready to totally change the way you develop in PHP. Some of the new features and updates include improved stack traces, execution traces to files, code coverage analysis and much improved remote debugging support. Xdebug’s documentation has also been rewritten for more clarity.
As with most open source projects, it’s very hard to know who are actually the users of the project. As I would like to know my users better, I would invite everybody who finds Xdebug useful to send me a postcard with their location. (Address is here at the top of the page). I am looking forwards to find out who you are!

还有款调试器也非常不错，历史比较悠久，就是NuSphere公司(老牌的PHP IDE开发商)开发的DBG，也可以集成到一些IDE开发工具中(例如：NuSphere PhpED、PHP Eclipse等)。