Xapian - Search Engine Library
Xapian is an Open Source Search Engine Library. It is written in C++, with bindings to allow use from Perl, Python, PHP, Java, Tcl, C# and Ruby. Xapian is a highly adaptable toolkit which allows developers to easily add advanced indexing and search facilities to their own applications. It supports the Probabilistic Information Retrieval model and also supports a rich set of boolean query operators.
It supports boolean, phrase and proximity, wildcard and synonym search. It is capable to perform related search by suggest more terms to the query text. Faceted search is supported. It has built-in filters to extract the content from various file formats like HTML, PDF, OpenOffice/StarOffice and lot more.
It also provides support to index data from the database like MySQL, PostgreSQL, LDAP etc.