DoxyGen is the best Unix tool for Documenting sources. It can generate an on-line documentation browser (in HTML) and/or an off-line reference manual from a set of documented source files. There is also support for generating output in RTF (MS-Word), PostScript, hyperlinked PDF, compressed HTML, and Unix man pages. The documentation is extracted directly from the sources, which makes it much easier to keep the documentation consistent with the source code.