Sooqr - Sooqr Search provides relevant and innovative site search engine for the website.
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.
Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.
Sumo - Free tools to grow your email list.
Hulbee Enterprise Search - Hulbee Enterprise Search is another powerful site search solution that intelligently retrieves information and documents regardless of their source or location.
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.