Guardian is a Open Source Software [Integrated Library System (ILS)] (http://en.wikipedia.org/wiki/Integrated_library_system). It is designed for schools or small libraries, so it is using Linux, Nginx, PostgreSQL and PHP / HHVM.
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Guardian is distributed under the GNU GPL version 3 or later. Please read the file LICENSE.md for more details.
To install or upgrade Guardian, please see the INSTALL.md file appropriate to your platform.