SmallSQL
The SmallSQL Database is a 100% pure Java DBMS for desktop applications. It has a JDBC 3.0 driver and supports SQL-92 and SQL-99 standards. It has a very small footprint of approx. 200KB for driver and database together. This is very small for a JDBC 3.0 interface.
The difference to other 100% pure Java databases is that it has no network interface and user management. The target applications are Java desktop applications. There is no installation required.
SmallSQL is released under the GNU LGPL.