Search Engines

BDDBot
A web robot, search engine and web server written in Java and available under GPL. Includes related resources. [Project no longer actively updated]
http://www.twmacinta.com/bddbot/

DataparkSearch Engine Tool
Open source search engine tool released under GPL and designed to organize search within a website, group of websites, intranet or local system.
http://www.dataparksearch.org/

Egothor
A cross-platform, full-featured text search engine written entirely in Java. It can be configured as a standalone engine, metasearcher, peer-to-peer HUB or used as a class library.
http://www.egothor.org/

KDE GUISearch
A tool for finding code by looking at the applications' GUI text messages (e.g., "Undo") and returning associated callbacks/slots (e.g., slotUndo()). Allows searching the KDE project CVS repository as a live demonstration.
http://guisearch.sourceforge.net/

Nutch
Effort to implement a prototype of an open source web-search engine.
http://lucene.apache.org/nutch/

OpenWebSpider
An open source web spider and search engine. Includes demo, source code and screenshots.
http://www.openwebspider.org/

Search Tools Listing: Open Source Search Engines
A listing of open source indexers, including links to related articles.
http://www.searchtools.com/tools/tools-opensource.html

Sphider
A lightweight search engine in PHP. Includes details of features, documentation, support forum, and download. [GPL]
http://www.sphider.eu/