Mole
SXML-based source code transformation tool which may be used for Literate and Elucidative Programming

l2t
(S)XML-enabled literate programming utility

Related links:
Peter Norvig's Tutorial on Good Lisp Programming Style
Literate Programming at the (La)TeX Navigator
literateprogramming.com
Javadoc
Literate XML/DTD programming
The Elucidative Programming Home Page
schemedoc: Scheme Documentation Generator of Project Schematics
Schemeweb