php_solr is a lightweight php client library for the Lucene-based enterprise search server Apache Solr.
OpenSearchServer is a powerful, enterprise-class, search engine program. Using its Web user interface, crawlers (Web, file, database, etc.), and REST/RESTFul API, you can integrate advanced full-text search capabilities into your application.
An online interactive tutorial and free text assesments.
A professional Web Content Management System.