DBIx::AnyDBD is a Perl module for developers writing cross database applications. It allows you to write "plugins" for different DBD drivers (Oracle, Sybase, etc) so that your application can do different things on different databases. It doesn't provide any compatibility layer - just an intelligent method to switch to the right class to use at runtime.
com.webprofusion.util.db.DBConnection is a simple wrapper Java object for JDBC database connections which is meant to help in building cross-DB SQL statements. It currently supports MySQL & MS SQL Server. It also includes the classes com.webprofusion.utils.StringUtils and com.webprofusion.SiteProperties. The dbconnection object currently uses thess classes to load settings for the DB Connection at runtime. This lets you define a properties file which specifies the dbengine and connection info.
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.
DB2 is a database management system that offers industry leading performance, scalability, and reliability on your choice of platform from Linux to z/OS. Its Web Control Center offers administrators an easy-to-use interface for maintaining databases, and can be run from any Java-enabled Web browser. For Java developers, DB2 UDB for Linux offers support for JDBC and SQLJ, and Net.Data allows for the creation of dynamic data diven Web applications. DB2 UDB for Linux allows you to harness the power of user-defined types and functions and support for Binary Large Objects.
DBPrism is an open source framework to generate dynamic XML from a database. It connects Oracle databases with Apache Cocoon, providing a high performance DBGenerator with functionality such as parallel content aggregation and ESI cache protocol. It also includes a powerlful database oriented CMS built on top of Apache Cocoon2 and DBPrism.