Optimizely - A/B testing you'll actually use.
Klevu - Klevu offers instant site search solution for eCommerce stores.
VWO - Use VWO to tweak, optimize & personalize your website with minimal IT help.
Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.
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.
Algolia - Algolia's Search API makes it easy to deliver a great search experience in your apps & websites. Algolia Search provides hosted full-text, numerical, faceted and geolocalized search.