DocIndexer:
http://www.methods.co.nz/docindexer/
DocIndexer is a toolkit for indexing and searching document directories. DocIndexer includes command-line utilities, Python index and search classes plus a Win32 COM server (for scripting from languages such as Visual Basic) that can be used to integrate indexing and searching into application software. The current version has built-in support for Microsoft Word, HTML, RTF, PDF and plain text documents.

Zebra:
http://www.indexdata.dk/zebra/
Zebra is a high-performance, general-purpose structured text indexing and retrieval engine. It reads structured records in a variety of input formats (eg. email, XML, MARC) and allows access to them through exact boolean search expressions and relevance-ranked free-text queries.

PHP/YAZ:
http://www.indexdata.dk/phpyaz/
Simpleserver:
http://www.indexdata.dk/simpleserver/
WebClarity BookWhere:
http://www.indexdata.dk/bookwhere/
http://www.webclarity.info/products/bookwhere.html
Z-Spy:
http://www.indexdata.dk/zspy/
ZAP!:
http://www.indexdata.dk/zap/

Z39.50 Resources:
http://www.niso.org/z39.50/z3950.html
http://www.loc.gov/z3950/agency/resources/software.html
http://www.lib.utah.edu/digital/ZContent.html
http://dli.grainger.uiuc.edu/

MarcEdit Z39.50 Client:
http://oregonstate.edu/~reeset/marcedit/html/help/marcedit4_5/html/yazMainAbout.html
Z39.50/PRISE 2.0:
http://www-nlpir.nist.gov/works/papers/zp2/zp2.html
JZKit 2:
http://developer.k-int.com/jzkit2/
ICONE:
http://www.crxnet.com/icone.php


FindItNow!
Disk and EMail Indexed Search Utility
ftp://ftp.simtel.net/pub/simtelnet/win95/txtutl/fin128.zip
via: http://www.bookcase.com/library/software/win9x.util.text.html

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Wilbur:
http://wilbur.redtree.com/
A free  file indexer, formerly commercial, now free and GPL, for Windows only at this time. Its an indexer, can index in zip files, and can handle PDF files.
via: http://svartling.hopto.org/index.php?q=Wilbur
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Lupy:
http://divmod.org/Home/Projects/Lupy/
Lupy is a is a full-text indexer and search engine written in Python. It is a port of Jakarta Lucene 1.2 to Python. Specifically, it reads and writes indexes in Lucene binary format. Like Lucene, it is sophisticated and scalable. Lucene is a polished and mature project and you are encouraged to read the documentation found at the Lucene home page.

Wordindex: Full text indexer and search engine
http://wordindex.sourceforge.net/
Wordindex is a full text indexing suite developed using perl as the backend and PHP as the web based search utility. Any language can be used to search as long as it has access to MySQL databases.
Wordindex is capable of indexing huge amounts of data, one production system has indexed over 14GB of textual, PDF, and compressed text files. Searches on that system are still less than a second on a modest server.
Wordindex is clusterable, the indexing process which can take a very long time to complete on a huge dataset (meaning ~10G+) can be run over a couple nodes to spread out the load.

Thales:
http://thales.sourceforge.net/

ViIndex:
http://viindex.sourceforge.net/

mindex - media indexer:
http://sourceforge.net/projects/mindex/
mindex is a multi-user client/server based media indexing tool, written entirely in C++. The gathered data about a media includes name, size, path and an md5sum of the files on it. This list is then sent to a server, which stores it in a database .

Fulltext indexer dmmFTSIndexerFile:
http://www.dmm.cz/en/dmmfts_2.htm

DeepSearch 4:
http://www.namo.com/products/deepsearch/

IDKSM Search Engine:
http://www.miraclec.com/software.html

Phantom 2.0 a quick, capable Web indexer:
http://www.searchtools.com/info/articles/in_phantom.html

Harddisk Search and Stats 1.0:
http://www.freebyte.com/harddisk_search_and_stats/
Freeware file and disk search engine. Harddisk Search and Stats can search multiple files and folders recursively. You can also specify non-recursive searches. Use as many search-phrases as you want within one search. The search can be filtered according to file extensions. The program has an internal file viewer, but you can also specify an external file viewer, or use the default Windows viewer, which can differ per file type. The search-filter can import all file extensions from a folder (recursively). The program does not need to be installed, and does not use the Windows registry. Simply double-click on the exe and the program starts! Harddisk Search and Stats is able to search all ASCII/text-based file types.


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Resources:
Developing a full-text indexer in Python
http://www-106.ibm.com/developerworks/linux/library/l-pyind.html
http://www.softlandmark.com/SearchEngine.htm
http://www.snapfiles.com/freeware/system/fwdiskcat_r.html
http://www.ir-ware.biz/locien.html
http://loosewire.typepad.com/blog/2004/08/a_directory_of__2.html

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PHP Directory Indexer:
http://indexer.sourceforge.net/

!!!!!!!!!!!!!!!!!!
AutoIndex PHP Script - A Website Directory Indexer:
http://autoindex.sourceforge.net/
http://prdownloads.sourceforge.net/autoindex/AutoIndex-1.5.1.tar.gz?download
!!!!!!!!!!!!!!!!!!

EXPOW:
http://membres.lycos.fr/explow/
EXPOW is a set of PHP scripts that generates directory indexes.
Replaces Apache directory autoindexer, or generates indexes "on the fly", with visualization facilities and file managing ability. 
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Harvest: A Distributed Search System
http://harvest.sourceforge.net/harvest/doc/

diskMETA - Internet search technologies for your desktop PC!
http://www.diskmeta.com/

Deductus:
http://www.aolej.com/dedu/

SearchWithin:
http://www.searchwithin.com/

blinkx:
http://www.blinkx.com/