Isearch is software for indexing and searching text documents.  It
supports full text and field based search, relevance ranked results,
Boolean queries, and heterogeneous databases.  Isearch can parse many
kinds of documents "out of the box," including HTML, mail folders,
list digests, SGML-style tagged data, and USMARC.  It can be extended
to support other formats by creating descendant classes in C++ that
define the document structure.  It is pretty easy to customize in this
way, provided that you know some C++.  A CGI interface for web based
searching is also included in the source distribution (but not
installed by default).
