c2man is an automatic documentation tool that extracts comments
from C source code to generate functional interface
documentation in the same format as sections 2 & 3 of the Unix
Programmer's Manual. It requires minimal effort from the
programmer by looking for comments in the usual places near the
objects they document, rather than imposing a rigid
function-comment syntax or requiring that the programmer learn
and use a typesetting language. Acceptable documentation can
often be generated from existing code with no modifications.