Dynatrace Load - Dynatrace Load lets you test the performance of web and mobile applications with the realism of load generation from the cloud.
Apache JMeter - Apache JMeter™.
Selenium - Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that.
Sitespeed - Sitespeed.io is an open source tool that helps to analyze and optimize website speed and performance.
locust - An open source load testing tool written in Python.
UbikLoadPack - UbikLoadPack provides plugins for Apache JMeter to load test Video Streaming, GWT Applications, Java Serialization based products and Flex.