Loader.io is a free load testing service that allows you to stress test your web-apps & apis with thousands of concurrent connections.

Unifying API testing, API Performance testing, API Mocks and UI testing.

WebLOAD – Performance and Load Testing for the Most Challenging Web Applications

Locust is an open source performance/load testing tool for HTTP and other protocols. Its developer-friendly approach lets you define your tests in regular Python code. Locust tests can be run from command line or using its web-based UI

Vigil is an open-source Status Page you can host on your infrastructure, used to monitor all your servers and apps, and visible to your users.

Cloud-scale performance testing. Effortless load testing and synthetic checks at scale. Cloud-native and open-source. The next evolution of performance testing.