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.