H2 is the Java SQL database which is very fast, open source, JDBC API, embeddable and small footprint.

Features

• Very fast, open source, JDBC API
• Embedded and server modes; disk-based or in-memory databases
• Transaction support, multi-version concurrency
• Browser based Console application
• Encrypted databases
• Fulltext search
• Pure Java with small footprint: around 2.5 MB jar file size
• ODBC driver