mnoGoSearch - http://search.mnogo.ru/
mnoGoSearch (formerly known as UdmSearch) is a full-featured Web search engine which you can use to build search engines over HTTP, FTP, and NTTP servers, local files, and database big text fields. It supports Oracle, MySQL, PostgreSQL, miniSQL, Solid, Virtuoso, InterBase, SAPDB, iODBC, EasySoft ODBC, and unixODBC database backends. mnoGoSearch is also known to work with MS SQL, SyBase, and Oracle through ODBC. C, CGI, PHP, and Perl WEB search frontends are included in the package.
Namazu - http://www.namazu.org/
Namazu is a full-text search system intended for easy use. Not only does it work as a small or medium scale Web search engine, but also as a personal search system for email or other files. Supported document types: HTML, Mail/News, MHonArc, RFC, TeX (with detex), man (with groff), Word (with wvWare), PDF (with pdftotext) and plain text.
Sary - http://sary.namazu.org/
Sary is a suffix array library and tools. It provides fast full-text search facilities for text files on the order of 10 to 100 MB using a data structure called a suffix array. It can also search specific fields in a text file by assigning index points to those fields.
Perlfect Search - http://perlfect.com/freescripts/search/
Perlfect Search is a Web site indexing and searching CGI application. Features include full-text and meta tag indexing, keyword weighting, relevance-ranked searches, dir/file excludes, stopwords, boolean searches, and an automatic installation and configuration utility that works with most Web server setups. It works on both UNIX and Windows NT.