Apache Solr - Solr is an open source enterprise search server based on Lucene search library, with XML/HTTP and...
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.
Websolr - Exterprise-grade search powered by open-source Apache Solr.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Decisiv Search - Decisiv is an enterprise search solution enabling users to search multiple repositories at once to access documents, projects etc.
Klevu - Klevu offers instant site search solution for eCommerce stores.