SGML

Comparison of SGML and XML
A Note from the W3C detailing the differences and similarities between the two markup languages.
http://www.w3.org/TR/NOTE-sgml-xml

A Gentle Introduction to SGML
An SGML FAQ in the context of the TEI e-text initiative and SGML application.
http://www-sul.stanford.edu/tools/tutorials/html2.0/gentle.html

Overview of SGML Resources
SGML links at the W3C, meant for use in reviews of the HTML specification.
http://www.w3.org/MarkUp/SGML/

SGMLtools-Lite
Formerly Linuxdoc-SGML, SGMLtools offers a out-of-the-box SGML processing solution for technical (DocBook) documentation. [Open source, GPL]
http://sgmltools-lite.sourceforge.net/

SP
A free, object-oriented toolkit for SGML parsing, validating, and entity management.
http://www.jclark.com/sp/

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. <small>(December, 1999)</small>
http://www.acm.org/crossroads/xrds6-2/women.html