DocBook is an XML vocabulary which enables you to create document content in a presentation-neutral form that captures the logical structure of the content. Using the DocBook Project XSL stylesheets, you can publish DocBook content as HTML pages and PDF files and other formats, including man pages, HTML Help, and JavaHelp.
TeXtrace is a collection of scripts that convert any TeX font into a Type1 .pfb outline font immediately suitable for use with dvips, pdftex, Acroread, and many other programs. The main advantage of using Type1 fonts with TeX is that Acroread renders TeX's bitmap fonts ugly on screen, but it renders outline fonts beutifully and fast.
java_syn.pl is a syntax highlighter for Java that converts a package of multiple .java files to multiple .html files. Class names are converted to links, so the reader can click on a class name to immediately see its source code. Default highlighting colors are the same as in Textpad.
Medoosa is a documentation tool for C++ that can produce UML class diagrams, including generalizations and associations. Corrections can be made interactively in a diagram editor (Dia) and are fed back into the source as Javadoc-style comments. The layout must still be done by hand.
adoC is a source code documenting system written in awk and shell script. It produces documentation in LaTeX format which resembles the Unix man pages. The documentation is generated from comment sections in the source code, which are marked by two special character sequences and internally divided into sub-parts by keywords. The system can be used with almost any kind of programming language.
XML-Lit is a simple program to perform very basic literate programming with any XML-based markup language. It uses James Clark's Expat XML parser to weave (convert to a form suitable for processing) and tangle (extract the source code from) your XML documents. It has only been tested with DocBook at the moment, but there is no reason why it should not work with any arbitrary XML markup.
DOC++ is a documentation system for C, C++, IDL, and Java. It generates both TeX output for high quality hardcopies and HTML output for sophisticated online browsing of your documentation. The documentation is extracted directly from the C/C++/IDL header/source files or Java class files.