Apache JMeter - Apache JMeter™.
Dynamic Yield - Personalization & customer experience management
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.
Optimizely - A/B testing you'll actually use.
locust - An open source load testing tool written in Python.
AB Tasty - AB Tasty is an all-inclusive platform for conversion rate optimization, personalization, customer activation, and testing.