Castor
Open source data binding framework for Java with support for XML, SQL, LDAP, and JDO.
eXist
eXist is an Open Source repository and retrieval engine for XML documents.
interBasis (IB 2.x)
SGML/XML-savy structured fulltext engine and multi-protocol information management system. (BSn)
Lore
Lore is a database management system (DBMS) for XML. The Lore executables are available for public use.
Xindice
DBMS written in Java to optimize the storage, retrieval, querying, and management of XML-based documents. Xindice was known as "dbXML Core" prior to joining the Apache XML Project.