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.
Nextopia - eCommerce Site Search & Navigation
Swiftype Site Search - Swiftype Site Search helps to sell more, get the right answer to more people on the platform and surface relevant content for readers and followers.
Sumo - Free tools to grow your email list.
UNBXD - eCommerce site search, navigation and personalization
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.