Optimizely - A/B testing you'll actually use.
CSS Scan - Instantly check or copy computed CSS from any element for only ~95$
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.
Hoverify - All-in-one browser extension to improve your web dev experience.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
Shuffle for Tailwind CSS - Tailwind CSS editor for busy developers