The SGML/XML Web Page:Database containing over 2000 documents pertaining to SGML, XML, and related standards. Features a bibliography for SGML, vendors and service providers, software reviews, mailing lists, user groups, and projects.
A Gentle Introduction to SGML: An SGML FAQ in the context of the TEI e-text initiative and SGML application.
Comparison of SGML and XML: A Note from the W3C detailing the differences and similarities between the two markup languages.
Overview of SGML Resources: SGML links at the W3C, meant for use in reviews of the HTML specification.
SGML: A Gentle Introduction: Tutorial from Text Encoding Initiative.
SGMLtools-Lite: Formerly Linuxdoc-SGML, SGMLtools offers a out-of-the-box SGML processing solution for technical (DocBook) documentation. [Open source, GPL]
SP: A free, object-oriented toolkit for SGML parsing, validating, and entity management.
Women Writers Project, ACM Crossroads Winter 1999: This article from Crossroads Winter 1999 issue describes the use of SGML to encode literature archives for research, written by B. Fan.