Rachel writes: "Now running at the Horowhenua Libraries Trust in New Zealand, is Koha, an open source, free library system written by Katipo Communications. It is a true library system, not just an OPAC, that runs as a public website, a library intranet and issues and returns via a telnet interface." That download link still isn't working tho... [the correct link to download is here (thanks Jeremy).]
The Free Library System (FLS) is a pure java implementation of a library system providing cataloging and circulation written by Dave Dunkin. FLS 0.1.1-2 presents as a java applet and is licensed with GPL and LGPL. The demo, specs, and goals are at the FLS homepage.
The Open Source Digital Library System (OSDLS, a.k.a. Powerful Yet TactfullyHelpful Electronic Arranger of Sources (PYTHEAS)) is a project to develop an open source next-generation library system. Current development includes a data model based on MARC and RDF expressed in XML. Links to the design draft and listserv details are at the OSDLS homepage.
Peter says: "Avanti version 0.1.3 has been released. This version allows the creation and management of multiple independent circulation systems, fixes a few bugs and includes improvements in the help command and code comments. Work is continuing on version 0.2 that will include an ARMS package. For more info. or to download the code go to www.nslsilus.org/~schlumpf/avanti.
I've now seen CDS/ISIS and its variants mentioned in several places and am still confused about what it is but here's a brief description nonetheless. from the UNESCO ISIS page: Micro CDS/ISIS is an advanced non-numerical information storage and retrieval software developed by UNESCO since 1985 to satisfy the need expressed by many institutions, especially in developing countries, to be able to streamline their information processing activities by using modern (and relatively inexpensive) technologies. The software was originally based on the Mainframe version of CDS/ISIS, started in the late '60s, thus taking advantage of several years of experience acquired in database management software development." take 2, from the CDS-ISIS user forum site: "Mini/Micro CDS/ISIS is a text retrieval program, designed and distributed free of charge by UNESCO. It is widely used for bibliographic (and other) databases throughout the world, and especially in developing countries." If I understand all this properly, it is basically a non-relational database environment commonly used by libraries and other largely nonprofits (20,000+ of 'em) throughout the world. I pulled down the unix version but can't quite make heads or tails of it. Somebody please explain more... update: collected comments from all who offered are available here.