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/

JXTA Search
   A distributed search system, designed for peer to peer networks and web sites.
   http://search.jxta.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/

Open Source Search
   Resources, ideas and news site for developing next generation open source search engines. Includes relevant source libraries and white papers.
   http://www.opensourcesearch.org/

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/