I don't know if it's the right section to post, because I am fairly sure that Doxygen (http://www.stack.nl/~dimitri/doxygen/index.html) is already portable. The program directory is around 12 MB with docs and GUI, and from the site is possible to download a "non-installer" version.
Anyway what is doxygen? Is a source code documentation tool. By putting some specially crafted comment inside your code, it is possible to generate reference documentation automatically. It works for Java, C/C++, PHP, Python and others
Give it a try