Lucene

Open-source search software

Snippet from Wikipedia: Apache Lucene

Apache Lucene is a free and open-source search engine software library, originally written in Java by Doug Cutting. It is supported by the Apache Software Foundation and is released under the Apache Software License. Lucene is widely used as a standard foundation for non-research search applications.

Lucene has been ported to other programming languages including Object Pascal, Perl, C#, C++, Python, Ruby and PHP.