Let me introduce you to the second project of the week after the Java automated test running JUnit. HSQLDB is one of the leading SQL relational database engine written in Java. The project offers a fast and simple database engine with in-memory, disk-based tables, supports embedded and server modes.
HSQLDB was launched in 2001 based on the HypersonicSQL database engine. The version 2.0, released in 2010, is mostly new code, written to conform to Standard SQL and JDBC 4 Specification.
Open Office, the well-known Open Source project, uses HSQLDB 1.8 as the integrated SQL database engine. HSQLDB is developing the integration of HSQLDB 2.0 for the future Open Office versions.
For comparison we estimate that, Derby, the Apache DB Subproject, is twice less reused than HSQLDB.
You can see on the left side, some of the most reused components of HSQLDB.