interBasis (IB 2.x) - SGML/XML-savy structured fulltext engine and multi-protocol information management system. (BSn) - http://www2.bsn.de/Z39.50/
Lore - Lore is a database management system (DBMS) for XML. The Lore executables are available for public use. - http://infolab.stanford.edu/lore/
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. - http://xml.apache.org/xindice/
eXist - eXist is an Open Source repository and retrieval engine for XML documents. - http://exist.sourceforge.net/