HyperSQL Database Engine
hsqldb is a relational database engine written in Java with a JDBC driver that supports a subset of ANSI SQL:1999. It offers a small, fast database engine. Embedded and server modes are available. It includes tools such as a minimal Web server, in-memory query and management tools (which can be run as applets or servlets, too), a test framework, PHP compatibility, Eclipse and NetBeans IDE compatibility, and a number of demonstration examples.