Apache XML project
Different open source tools, most of which use the Xerces implementation (DOM Level 1 & 2) as a base. Xerces itself is available in Java, C++, Perl, and COM.
David Baron's DOM Tests
Tests in JavaScript for compliance with some parts of the W3C DOM specs.
DocZilla - an SGML/XML browser
Built on Mozilla code, this browser has the same support for the DOM as Mozilla does.
Mozilla - XML/HTML browser
An open-source XML/HTML browser which is implementing full Level 2 DOM support.
Oracle XML Developer's Kit
Contains a parser with a Level 1 DOM interface. Available in Java, C, C++ and PL/SQL.
Oracle XML Transviewer Beans
DOM Java Bean encapsulation for use in quickly developing GUIs to XML applications.
The Gnome DOM Engine
Promises to create a fully standards-compliant DOM interface. It is based on Daniel Veillard's libxml.
XML4P Perl DOM
Includes a collection of Perl5 wrapper objects that internally use their XML4C counterparts for Level 1 DOM processing.
xmlBlaster
XML and CORBA/RMI/XML-RPC based MOM (message oriented middleware) for Java/C/C++/Perl/Tcl/Python. Free for commercial and non commercial use (LGPL).