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