Proprietary

OpenLink Virtuoso
A cross-platform, Internet data integration server, implementing native XML storage, web, file, and database server functionality and universal data access middleware as a single server solution.
http://www.openlinksw.com/virtuoso/

TEXTML
native XML database server for content search and retrieval, supports WAP
http://www.ixiasoft.com/

Xenos Group, Inc.
Provides data and electronic document transformation solutions.
http://www.xenos.com/

X-Hive/DB
XML Database in form of a Java-based persistent DOM implementation.
http://www.xhive.com/

Xyleme
Dynamic data warehouse that is an indexed XML repository capable of answering queries from applications and users.
http://www.xyleme.com/