Loader.io - Loader.io is a simple cloud-based load testing service
Apache JMeter - Apache JMeter™.
WebLOAD - WebLOAD - The most flexible and cost effective software for enterprise load, stress and performance testing, integrated with DevOps processes. Click for details
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.
locust - An open source load testing tool written in Python.
k6 Cloud - Managed load testing service built on top of the popular open-source project k6.