FirePHP – Debugging PHP applications with Firebug
FirePHP seems like a very cool project, allowing PHP developers to debug applications without having to disrupt the normal process of a script. It works by sending the debug content to the browser in special HTTP headers, and the Firefox extension add-on to Firebug will parse those and display them in a special panel within Firebug.
It’s so useful I’m going to install this right now. I can’t believe nobody else thought about doing this before!