db4o is an object database for Java and all .NET environments. Its features include ACID transactions, automatic class schema recognition, query-by-example, a S.O.D.A. object querying API, native queries, LINQ support on .NET, callback methods, memory files, cascade-on-delete, multi-threaded access, and Java Webstart and servlet support.
MUSCLE (Multi User Server Client Linking Environment) is an N-way messaging server and networking API. It includes client-side networking APIs for various languages, including C, C++, C#, Delphi, Java, and Python. MUSCLE lets programs communicate over a network via streams of serialized Message objects. The included server program ("muscled") lets its clients message each other and store information in its server-side hierarchical database. The database supports flexible queries via hierarchical wildcarding, and "live" updates via a subscription mechanism.
MaVerick is a MultiValue database management system. MultiValue databases are said to be one of the computer industry's best kept secrets. First appearing over 30 years ago as PICK, they have continued to evolve through various commercial vendors, and are still in active development today. They are very resource friendly, are incredibly fast, feature a very user friendly data retrieval and reporting language (variously called ACCESS or English), and a rapid application development language based originally on Dartmouth Basic. The MaVerick project is an attempt to create an open source variant, written in Java.
OpenIsis provides a library and tools to access CDS/ISIS databases, which are mostly used for bibliographic data (ISO2709, Z39.50) but also well suited for other catalogues due to the very flexible indexing mechanism. Based on a C library, there are also bindings for Perl and Java (Tcl to come).
CloverETL is Java-based tool/framework for data integration and creation of data transformations. It is component based and follows the concept of transformation graphs which consist of individual nodes/components performing simple (or complex) operations on data. Any transformation can be defined as a set of interconnected nodes through which data flows. CloverETL can be used as a standalone application or be embedded into a larger project.
ObjectDB for Java/JDO is a powerful yet compact Java Data Objects (JDO) Object Database (ODBMS), written entirely in Java, and compliant with the Java Data Objects (JDO) standard developed by Sun (JSR12). ObjectDB for Java/JDO is designed to efficiently handle databases of various sizes, ranging from a few KBs to hundreds of GBs. Among its features are small footprint, high performance, rapid development, easy deployment, and flexible architecture (1-Tier, 2-Tier, or N-Tier).
Sequoia provides high availability and performance scalability for databases. It is is the continuation of the C-JDBC project. It provides transparent database clustering (partitioning, replication, etc.). It works with any Java application without code modification and with any database engine. It has been successfully tested with Tomcat, JBoss, JOnAS, WebSphere, MySQL, PostgreSQL, Apache Derby, HSQLDB, SAP DB, Oracle, DB2, Sybase, MS SQL Server, Firebird, and more.