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. It 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++ (and you will need to ftp the source code). A CGI interface is also included for Web based searching.