Xtce.com

Free or Cheap Web Authoring - Validation
Mark Freeman on free or cheap web authoring featuring HTML, META Tag, Cascading Style Sheet, accessibility and link validation.
home.columbus.rr.com/

Systemwire xlinkit
integrity management of distributed XML data. Provides a validation rules language and processing engine that allows constraints beyond schema and DTD validation.
www.systemwire.com/

Trang
A open source multi-format schema converter based on RELAX NG. Includes documentation and download.
www.thaiopensource.com/

Schemachine
Specification of a framework for modular validation of XML documents.
www.topologi.com/

XML Well-Formedness Checker and Validator
Checks an XML document (specified by URL) for well-formedness and optionally DTD-based validity and namespace correctness. Outputs canonical XML. Runs over the web and can be downloaded.
www.cogsci.ed.ac.uk/

Comparative Analysis of Six XML Schema Languages
Paper by Dongwon Lee and Wesley W. Chu comparing XML DTD, XML Schema, XDR, SOX, Schematron, and DSD.
www.cobase.cs.ucla.edu/

XML Validation
Web-based XML validator that produces easy to read error messages and asks for missing files (e. g., XSD) if necessary.
xmlvalidation.com/

Independent Verification &Validation Facility
The NASA IV&V Facility provides the highest achievable levels of safety and cost-effectiveness for mission critical software.Their efforts have contributed to the improved safety record of NASA since its inception.
www.ivv.nasa.gov/

Validation Service for RELAX NG
An online RELAX NG validation service. Supports multiple schemas at a time.
hsivonen.iki.fi/

MO BIO Laboratories Certification and Validation Services Group
Laboratory Services offer testing and certification programs for bioburden and sterilization, in Carlsbad, Calif., USA.
www.mobio.com/