Apache Solr - Solr is an open source enterprise search server based on Lucene search library, with XML/HTTP and...
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Websolr - Exterprise-grade search powered by open-source Apache Solr.
Coveo - Enterprise search technology for better customer support, customer self-service, and knowledge management in the digital workplace.
Decisiv Search - Decisiv is an enterprise search solution enabling users to search multiple repositories at once to access documents, projects etc.
Lookeen - Lookeen is an enterprise search and desktop search software designed for individuals and enterprises. Its key function is Outlook search.