Xtce.com

W3C Official Public Site for XML Schema
Contains status information, links to specifications and tools that implement XML Schema
www.w3.org/

XML Schema Reference at Zvon
A complete hyperlinked reference for XML Schema which can be downloaded for offline use.
www.zvon.org/

W3C XML Schema Test Collection
Collection of test schemas used to ensure consistency among XML Schema implementations.
www.w3.org/

SOX - Schema for Object-Oriented XML 2.0
A schema language for defining the syntactic structure and partial semantics of XML document types; an alternative to XML DTDs. [W3C Note 30 July 1999]
www.w3.org/

xmlDraft
an intuitive XML Schema editor, displaying a realtime treeview mockup of what the Instance XML Document should look like while editing the XML Schema
www.sysonyx.com/

xmlBlueprint
XML editor of XML documents, DTDs and XML Schemas.
www.xmlblueprint.com/

XSBrowser
Open source browser that creates a human readable document model from a given DTD or XML schema.
www.lumrix.net/

XMLFox freeware XML/XSD Editor
Freeware graphical XML editing and validation tool for creating valid, well-formed XML documents and/or XSD Schema.
www.xmlfox.com/

Simple Sample DTD/XML 1.0 Generator
An interactive online tool for experimenting with DTDs, XML, and XML schemas. Requires a Javascript enabled browser.
rtiess.tripod.com/

Popkin Software XML Architect
A graphical XML schema editor. Site offers product benefits and information.
www.popkin.com/