JYD Object Database is a pure Object DBMS written entirely in Java for use
by Java applications. The product is a multi-user system with client/server
support and garbage collection on the database. It includes a web server
supporting servlets, and it is compatible with any other servlet engine or
application server.

With the release of Mac OSX, JYD immediately became available to Mac
developers (it requires Java 2). Now JYD 2.0 has been released with even
more features, including database event notification, remote method
invocation, and distributed databases. A free eval with a 65 page manual is
available at (http://www.jyd.com)