AlgebraDB
A Java-based, experimental relational database representing functions as infinite tables. [Open Source, LGPL]
url: algebradb.sourceforge.net/
Axion
A small, fast, SQL and JDBC compliant relational database engine written in and for the Java programming language. [Open source, BSD License]
url: axion.tigris.org/
CodeBase
Relational database engine supporting multiple platforms (UNIX, Windows, MacOS) and multiple programming languages (Java, C/C++, Visual Basic, VBScript/ASP, C#). Supports client/server, embedded and micro (J2ME, PocketPC) environments. [Commercial]
url: www.sequiter.com/products/
Daffodil DB
A embeddable, SQL-99 specification compatible, Java-based database engine. [Commercial]
url: www.daffodilwoods.com/
Hypersonic SQL
RDBMS with JDBC interface, client-server version, query tool, grid, tree, performance test class, servlet, and self-test program. [Open Source, BSD-like]
url: hsqldb.sourceforge.net/
Infinity Database Engine
An embeddable datastore with data compression, global transactions, integrity preservation, high concurrency, and flexible, extensible data model. [Commercial]
url: boilerbay.com/infinitydb/
JavaDBF
A Java library for reading and writing Xbase (dBase/DBF) files. [Open source, LGPL]
url: sarovar.org/projects/javadbf/
Mckoi SQL Database
Multi-client / multi-threaded SQL relational database management system written in Java. Includes JDBC 2.0 driver. [Open Source, GPL]
url: www.mckoi.com/database/
MindLab - Developer Site
Student project to create a relational database in Java. [Freeware]
url: www.stormpages.com/mindlab/
PointBase
Pure Java RDBMS with a JDBC interface including client/server, embedded, and micro (J2ME) products. [Commercial]
url: www.pointbase.com/home.shtml
QED
Small footprint database with transactions, failure recovery, SQL 92 conformance plus many SQL3 features. [Commercial]
url: www.quadcap.com/home.html
RedBase Pure Java RDBMS
Pure Java RDBMS with a JDBC interface. [Commercial]
url: www.bungisoft.com/html/products/redbase/redbase.ht...
Smyle
(Storage That Makes Your Life Easier) An open source hierchical/relational database, seamlessly integrated with Java. [Open Source, GPL]
url: www.drjava.de/smyle/
tinySQL
A very lightweight 100% Java text SQL engine that includes a JDBC driver. [Open Source, LGPL]
url: www.jepstone.net/tinySQL/
Tomato DBMS
A suite of tools around a relational database management system with multimedia features. [Freeware, No Source Code]
url: tomato4j.hypermart.net/
xBaseJ
A dBASE III & IV compatible Java database. [Commercial]
url: www.americancoders.com/xBaseJ/