KOHA is the best and free library managment system for any scale library.

Koha installation is little challange for system administrators.
It written by perl language and run on apache server with mysql backend databasse.
latest stable version is v3.4

following is their announcement

Koha 3.4

Koha 3.4 Released
by Chris Cormack

Kia ora tatou
The Koha development team is happy to announce the release of Koha 3.4.0.
Koha 3.4.0 is a major feature release that contains major changes to underlying architecture (adoption of Template::Toolkit for templating) and performance enhancements (removal of item data from biblio records).
These changes, in addition to the inclusion of many new features, mean a lot of new strings for translators to translate.
For these reasons we recommend that people who are already running Koha inproduction delay their upgrade until 3.4.1, due May 22, to give the translators time to finish, and for the removing of item data to be streamlined. If you do wish to upgrade please make sure you read the UPGRADE section of the INSTALL document.
The development team would like to thank all the people who have made this release possible. Please take time to read the release notes.

http://koha-community.org/koha-newsletter-volume-2issue-4-april-2011/#release