Apache Solr - Solr is an open source enterprise search server based on Lucene search library, with XML/HTTP and...
Xobni - Xobni provides effortless email and address book management and search for Microsoft Outlook and BlackBerry. Put a face to every name. Lightning fast Outlook Search.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Live Inbox - Live Inbox is a Microsoft Outlook plugin that helps you organize your email and search your inbox.
Coveo - Enterprise search technology for better customer support, customer self-service, and knowledge management in the digital workplace.
X1 Search - X1's Lightning-Fast Search Software. Premium Alternative to Windows Desktop and Outlook Search.