OPACIAL is an open source Web 2.0 Online Public Access Catalogue (OPAC). It is based on PHP-Mysql (requires Yaz and GD). The users can insert their own social tags/opinions and have a faceted search/browse interface (also using social tags).

Kramerius is a digital Library based on Fedora Commons. It is being developed and used by Czech libraries.

This librarian project aims to collect images of book cover pages allowing users (libraries) to integrate them to their WebOPAC. Particular images are acquired by scanning book covers by participating libraries or downloaded from co-operating publishers. The project has been developed and is being used by a large number of Czech libraries - its main strength being its collaborative nature.

OpenBiblio is an easy to use, automated library system written in PHP containing OPAC, circulation, cataloging, and staff administration functionality.

Joomla is an award-winning content management system (CMS), which enables you to build Web sites and powerful online applications. Many aspects, including its ease-of-use and extensibility, have made Joomla the most popular Web site software available. Best of all, Joomla is an open source solution that is freely available to everyone.

The Net::Z3950 module provides a Perl interface to the Z39.50 information retrieval protocol (aka. ISO 23950), a mature and powerful protocol used in application domains as diverse as bibliographic information, geo-spatial mapping, museums and other cultural heritage information, and structured vocabulary navigation.

MULtifacet is a Drupal 5 module that wraps a UI around an arbitrary Solr index.

This is a basic substitute for expensive library software. It will require you to manually enter all the titles, authors, and ISBN-13s into a database at first, but after that maintenance is easy.

LibraryFind is an open source metasearch application developed by librarians for libraries, built with Ruby on Rails.

Some Current Features:

libxess is a collection of server-side proxies that provide a Marc-XML/REST based interface to the records and holdings of legacy catalogs such as Innopac/III Millennium.

libxess consists of a web service API and a set of implementations.

The web services API is based on unAPI.