Optimizely - A/B testing you'll actually use.
Loader.io - Loader.io is a simple cloud-based load testing service
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
WebLOAD - WebLOAD - The most flexible and cost effective software for enterprise load, stress and performance testing, integrated with DevOps processes. Click for details
Google Analytics - Improve your website to increase conversions, improve the user experience, and make more money using Google Analytics. Measure, understand and quantify engagement on your site with customized and in-depth reports.
StresStimulus - Load testing tool for websites and mobile that works with hard-to-test applications.