Optimizely - A/B testing you'll actually use.
Edit - Edit any website, no code required
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.
Flagsmith - Flagsmith lets you manage feature flags and remote config across web, mobile and server side applications. Deliver true Continuous Integration. Get builds out faster. Control who has access to new features. We're Open Source.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
Edit Any Webpage - Edit any site on the fly - bookmarklet