Evergreen - Highly-scalable software for libraries that helps library patrons find library materials, and helps libraries manage, catalog, and circulate those materials. (Source Code) GPL-2.0PLpgSQL
Koha - Enterprise-class ILS with modules for acquisitions, circulation, cataloging, label printing, offline circulation for when Internet access is not available, and much more. (Demo, Source Code) GPL-3.0Perl
RERO ILS - Large-scale ILS that can be run as a service with consortial features, intended primarily for library networks. Includes most standard modules (circulation, acquisitions, cataloging,...) and a web-based public and professional interface. (Demo, Source Code) AGPL-3.0Python/Docker