Solution I: Use a format that translates to many

• Sphinx can do nice HTML, LaTeX, epub, (almost) plain text, man pages, Gnome devhelp files, Qt help files, texinfo, JSON
• Markdown can do LaTeX, HTML, MS Word, OpenOffice, XML, reStructuredText, epub, DocBook, ... but not Sphinx
• IPython notebook: can do LaTeX, reStructuredText, HTML, PDF, Python script
• Sphinx and Markdown has some limited math support