A simple lightweight markup language like e.g. defined by Creole 1.0 could be very useful for use in program and application documentation that is used as the basis for automatically created HTML and LaTeX. Is there any Java library out there that would be able to create HTML AND LaTeX from some markup dialect (creole, markdown, textile or similar)?
Are there any tools or libraries that would make it easier to implement such a library oneself? Starting from scratch gets surprisingly complex when done right.
Unless I've misunderstood your question, Fletcher Penney's Multimarkdown is about a comprehensive as you'll get for a markup language, and there appear to be a number of Java implementatons. HTML creation is standard and more fully-featured than the original Markdown (e.g. tables, definition lists), but Fletcher has also thought a lot about LaTeX.
There's also a useful community, which might help with further details.