QED is a pure Java database that features:
Pure Java: a high performance, small footprint, zero-administration database, perfect for embedding with your application.
A full set of RDBMS features: transactions, data integrity, failure recovery, comprehensive SQL 92 conformance plus many SQL3 features.
Support for JDBC 2.0
Open source, free software, with a single-price UNLIMITED seats commercial redistribution license available.
QEDs pure Java engine provides very high performance, since database accesses can be performed locally, without the necessity of a network round trip for every operation. Conventional JDBC drivers, no matter how fast the back-end database, incur network overhead -- frequently the bottleneck in a database application. A configurable in-memory cache also helps boost performance by reducing disk operations.