Lotame - Make your data actionable, learn about your most valuable customers, improve ROI by targeting the right audience and increase relevance across screens.

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.

Adobe Audience Manager - Adobe Audience Manager is a data management platform that integrates online and offline data to deliver a unified view of all your audiences

Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.

Google Audience Center - 3 votes and 6 comments so far on Reddit

ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.