Loader.io - Loader.io is a simple cloud-based load testing service
Apache JMeter - Apache JMeter™.
LoadFocus - Cloud Testing Infrastructure | Cloud Testing Services and Tools for Websites & APIs.
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.
Loadium - Performance Testing & Load Testing Tool
locust - An open source load testing tool written in Python.