SearchBlox - SearchBlox is an out-of-the-box Enterprise Search Solution built on top of Apache Lucene/Solr.
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.
Hulbee Enterprise Search - Hulbee Enterprise Search is another powerful site search solution that intelligently retrieves information and documents regardless of their source or location.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Varonis DatAnswers - Varonis DatAnswers is a leading enterprise search and discovery platform that deliver secure and relevant searches for authorized NAS, Windows files servers and share point users.
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.