Optimizely is a lower cost entry tool for anyone looking to do website testing. While their pricing structure has changed over the years it still is a pretty cost effective solution. It is easy to get tests up and running within 5 minutes once you have code placed on your site.
I love the drag and drop features of Optimizely. It makes it very easy to make simple changes to do landing page testing for my paid search campaigns. It also frees up dev time for our web team. Also, The findings from Optimizely tests are so valuable for an end customer experience.
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.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
DevTest - Test management solution for efficient quality assurance
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.
Beta Testing - Beta Testing is an all-in-one feature-rich technical testing solution created to help small to large size businesses test and enhance their products through insights.
AB Tasty - AB Tasty is an all-inclusive platform for conversion rate optimization, personalization, customer activation, and testing.