Evergreen is a full-featured, open source, integrated library system product that was originally designed for consortia.  

History
Evergreen was developed by, and went live with Georgia PINES in September of 2006. Georgia PINES released the code under a GPL license and it has been growing ever since. More on Georgia PINES and Evergreen history is available at http://evergreen-ils.org/dokuwiki/doku.php?id=faqs:evergreen_faq_1.

Official WebsiteThe official project pages located at http://evergreen-ils.org/.  There you can find the Evergreen Roadmap that documents some of the features added for each release and indicates those planned for future releases. 

Demo Servers
Several demo servers are available.  Links and instructions are available at http://evergreen-ils.org/dokuwiki/doku.php?id=community_servers#community_demo_servers.

Developers
If you are developer and want to get right into the code, you'll find the code repository at http://svn.open-ils.org/trac/ILS/ and instructions for contributing code at http://evergreen-ils.org/dokuwiki/doku.php?id=contributing.