SoftQuad is a leading developer of software for SGML and provider of related services. Their initial popular product is Author/Editor, a WYSIWYG tool for creating and editing SGML documents. To work with a new class of documents, use RulesBuilder to convert a Document Type Definition to a file of rules that will work with A/E.
For the WWW they provide HoTMetal in free demo form or for Professional Use.