Open source search engine library written in C++, with bindings to allow use from other languages as well.

Effort to implement a prototype of an open source web-search engine.

A lightweight search engine in PHP. Includes details of features, documentation, support forum, and download. [GPL]

A distributed Web crawler and caching HTTP/HTTPS proxy built on the principles of peer-to-peer (P2P) networks.

Web crawler based on Lucene, Apache Tomcat, Java Server Faces and JBoss RichFaces. News, product information, documentation, download, and discussion forums.

A listing of open source indexers, including links to related articles.

Open source, cross-platform distributed crawler. FAQ, documentation and a support forum.

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.

Open source search engine tool released under GPL and designed to organize search within a website, group of websites, intranet or local system.

A .NET web crawler written in C# using SQL 2005 and Lucene. Documentation and online demonstration.