In his latest post Rob Allen gives a "first look" at a new feature in the Zend Server (v7) product from Zend - Z-Ray. The z-Ray feature gives you a complete "under the covers" look at what your code is doing including resource use, database connections and processing time.
I've been running the beta for all my development work for a while now and the main reason is the new Z-Ray feature. Z-Ray is a bar that is injected into the bottom of your page showing lots of useful information.
His post shares some of the results he found with his development version of Joind.in and screenshots of the results. He shows the levels of detail available at each level, all directly in the browser. It even includes functionality to track all variables being created or used in the current execution.