HSQLDB (HyperSQL DataBase) is the leading SQL relational database engine written in Java. It offers a small, fast multithreaded and transactional database engine with in-memory and disk-based tables and supports embedded and server modes. It includes a powerful command line SQL tool and simple GUI query tools.
For more information see http://hsqldb.org/
To make the driver accessible to JDBC and ActiveRecord code running in JRuby :
require 'jdbc/hsqldb' ::.
For backwards compatibility with older (<= 220.127.116.11) versions of the gem use :
require 'jdbc/hsqldb' ::.(:require) if ::.respond_to?(:load_driver)
Copyright (c) 2013 The JRuby Team.
HSQLDB is completely free to use and distribute under a license based on the standard BSD license and fully compatible with all major open source licenses. see LICENSE.txt and http://hsqldb.org/web/hsqlLicense.html for more details.