HSQLDB

HSQLDB is a relational database engine written in Java, with a JDBC driver, supporting a rich subset of ANSI-92 SQL. It offers a small (less than 160k), fast database engine which offers both in memory and disk based tables. Embedded and server modes are available. Additionally, it includes tools such as a minimal web server, in-memory query and management tools (can be run as applets) and a number of demonstration examples. The product is currently being used as a database and persistence engine in many Open Source Software projects and even in commercial projects and products. This product includes HypersonicSQL.