Does anybody know a widely used and open source project using literate programming? (Edit: please include only programs expressed "as a web of ideas" that Knuth mentions - apparently otherwise it's not literate programming, just loads of inline documentation?)

From what I've seen, literate programming is great in theory and worse than useless in practice. It's so far away from reality. I have had the misfortune of working on a FunnelWeb codebase, and it was one of the most incomprehensible codebases I've ever seen.

Preprocessing the code is an awful step in any language. Somehow, the "not documentation" still goes out of date. There are several other problems, explained at [0] better than I can in a comment.

Specifically about this project: While I enjoy writing blogs in markdown because of its constraints, reStructuredText (reST) is more powerful/expressive (by design). Because you can easily express semantics/relationships, the resulting links in the generated documentation make the "web" of source code easier to navigate - something Knuth was trying to do with literate programming.

[0] http://akkartik.name/post/literate-programming