Apache Derby is a subproject of the Apache DB project.
You can find Derby on the web at:

http://db.apache.org/derby/

Apache Derby releases can be downloaded from the following page:

http://db.apache.org/derby/derby_downloads.html

Derby is a pure Java, standards-based relational database engine.
Derby aims to be an easy to use solution for data management for
software developers with zero administration for end users.

The 10.1 release includes a new open source network client driver, as
well as a number of other new features and enhancements:

    * Support for J2ME/CDC/Foundation with JSR-169 JDBC subset
    * Online compress functionality for reclaiming disk space during
operation
    * XA support for Network Server
    * Increased identifier lengths to 128 characters for all identifiers
    * Added SQL: INTERSECT and EXCEPT
    * Added SQL: SYNONYM
    * JDBC Updatable Result Sets
    * ORDER by expressions
    * Allow insertions into an identity column
    * Support for explicit Java method signature in function and
procedure definitions


See the CHANGES file for a list of changes in the lastest snapshot or release distribution of 10.1.