Wikipedia
OpenSearchServer is an open source application server allowing development of index-based applications such as search engines. Available since April 2009 on SourceForge for download, OpenSearchServer was developed under the GPL v3 license and offers a series of full text lexical analyzers. It can be installed on different platforms (Windows, Linux, Macintosh).
While it started as an in-house project by a private media group, OpenSearchServer is now supported by Jaeksoft, a commercial company launched in February 2010. Jaeksoft provides services and roadmap guidance for OpenSearchServer.
The main features of OpenSearchServer are : An integrated crawler for databases, web pages and rich documents; a user-friendly GUI allowing development of most applications through a web page interface built in Zkoss; snippets; faceting; an HTML renderer for integrating search results in a page; and monitoring and administration features.
OpenSearchServer is written in Java and it can be integrated into almost any kind of application without the need to produce Java code. REST/XML APIs make OpenSearchServer connectable to other programming languages. The "advanced plugins" capability allows sophisticated customizations.
OpenSearchServer is currently available in version 1.2.3 rc2 and it is considered stable by the developers community. Version 1.1, launched in April 2009, reached the SourceForge top 15, with wide press coverage and many new users worldwide.