mod_oai is an Apache module

Apache HTTP Server

The Apache HTTP Server, commonly referred to as Apache , is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone...

 that allows web crawler

Web crawler

A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner or in an orderly fashion. Other terms for Web crawlers are ants, automatic indexers, bots, Web spiders, Web robots, or—especially in the FOAF community—Web scutters.This process is called Web...

s to efficiently discover new, modified, and deleted web resources from a web server by using OAI-PMH, a protocol which is widely used in the digital libraries

Digital library

A digital library is a library in which collections are stored in digital formats and accessible by computers. The digital content may be stored locally, or accessed remotely via computer networks...

 community. mod_oai also allows harvesters to obtain "archive-ready" resources from a web server.

The mod_oai project is housed at Old Dominion University

Old Dominion University

Old Dominion University is a state university located in Norfolk, Virginia, United States, and is accredited by the Southern Association of Colleges and Schools...

 under the direction of Michael L. Nelson. mod_oai is developed under the GNU General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

(GPL), and is distributed free of charge.