Separately or in combination with faceted navigation mindsteps delivers full website search (with auto-complete) based on:
Apache Lucene
From Wikipedia, the free encyclopedia
Apache Lucene is a free/open source information retrieval software library, originally created in Java by Doug Cutting. It is supported by the Apache Software Foundation and is released under the Apache Software License.
Lucene has been ported to other programming languages including Delphi, Perl, C#, C++, Python, Ruby and PHP.
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Google Search Appliance
For Medium & Large Business The Google Search Appliance provides robust, scalable and secure search across virtually all the information in your company. Taking Google’s core search technology and optimising it for business use, the Google Search Appliance provides universal search across a variety of 
internal and external sources – including file shares, intranets, databases, applications, hosted services and content management systems. The Google Search Appliance makes all the information that employees need to be productive accessible through a single easy-to-use search box. The latest version adds key new features around search quality, access control and connectivity.