XHProf: A Hierarchical Profiler for PHP

XHProf is a function-level hierarchical profiler for PHP and has a simple
HTML based navigational interface. The raw data collection component is
implemented in C (as a PHP extension). The reporting/UI layer is all in
PHP. It is capable of reporting function-level inclusive and exclusive wall
times, memory usage, CPU times and number of calls for each function.
Additionally, it supports ability to compare two runs (hierarchical DIFF
reports), or aggregate results from multiple runs.