Loader.io - Loader.io is a simple cloud-based load testing service
Dynatrace Load - Dynatrace Load lets you test the performance of web and mobile applications with the realism of load generation from the cloud.
Loadium - Performance Testing & Load Testing Tool
Apache JMeter - Apache JMeter™.
LoadFocus - Cloud Testing Infrastructure | Cloud Testing Services and Tools for Websites & APIs.
Sitespeed - Sitespeed.io is an open source tool that helps to analyze and optimize website speed and performance.