Apache JMeter - Apache JMeter™.
Loader - Load testing and tracking application
Blackfire.io - Blackfire empowers all PHP developers and IT/Ops to continuously verify and improve their app’s performance, throughout its lifecycle, by getting the right information at the right moment.
Sitespeed - Sitespeed.io is an open source tool that helps to analyze and optimize website speed and performance.
WebLOAD - WebLOAD - The most flexible and cost effective software for enterprise load, stress and performance testing, integrated with DevOps processes. Click for details
XRebel - XRebel is a lightweight Java profiler that helps developers find and fix common problems in their application as they code.