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.
Epydoc is a tool for generating API documentation for Python modules, based on their inline documentation strings (docstrings). It produces HTML output (similar to the output produced by Javadoc) and LaTeX output. It supports four markup languages for documentation strings: Epytext, Javadoc, ReStructuredText, and plain text.
Ccdoc is a Javadoc-inspired tool that automatically generates HTML Web documentation from C++ programs by parsing the source file headers. It was designed to aid the collaboration between package users and package developers. It runs on FreeBSD, Linux, Mac OS X, Solaris, and Windows (98, 2k, Me, and XP).
TEKlib is a library and operating system effort. It runs hosted on platforms such as Unix and Windows. It can serve as a freestanding operating system on architectures such as the Playstation 2. It is also a middleware that provides a constistent interface across all hosting environments. Its freestanding nature, small footprint, and absence of global data recommend it as a layer for portability and code reuse in heterogeneous environments.
Tartan is a text parsing engine targeted at wiki text. The syntax specification is defined in YAML in the form of regex-based rules. It supports layering and multiple output types. Rules for Markdown to HTML are included, with optional layered extensions for tables. It is implemented in Ruby, but looking to have implementations in other languages.