Every PHP application you start will surely have a couple of bugs at the end (except if your God or something) and then debugging starts. There are a lot of PHP debuggers out there and they are pretty good also but usually they are hard to install and configure.
So, I found an alternative for PHP debugger software called PHP bug lost. Lets detail a bit about it. First of all, the PHP debugger script has only one file (no dependencies) and its very easy to configure. You simply need to include the file in your script and your ready to go. Second of all, the PHP debugger offers a lot of things you can track. You can send log messages, view SQL queries (it automatically sends an email to the admin if there are any errors), measure times and memory usage (again, sends an email to the admin for long loading times or excessive memory usage), see all vars in your script but also AJAX queries.
The single-file PHP debugger script can run both in a console or monitor. You can use it like a console when developing sites to help you with your daily work and as a monitor for production sites where you want to track the errors, load times, etc.
The PHP debugger is an open source project so feel free to improve it, etc