WEB and its relatives rely on a programming language (eg. C) and a document formatting language (eg. TeX). The program and its documentation are written at the same time, in an unique source file. At anytime, one can extract the whole source files (aka 'tangling') or the documentation explaining its implementation (aka 'weaving').
Have you ever used literate programming? What is you experience with it?
[1] http://www.literateprogramming.com/knuthweb.pdf