I've had quite a few requests for better docs in Cohttp/Async, and so the latest version includes a little Hello World webserver that serves local files via HTTP (like Python's SimpleHTTPServer does).
https://github.com/avsm/ocaml-cohttp/blob/master/bin/cohttp_server_async.ml
It's included in cohttp-0.9.14 and installed if you do "opam install async cohttp" and run via "cohttp-server". It uses Command.async_basic to configure port/htdoc-dir and so forth.
I'm hoping to write a full tutorial before 1.0, but any external contributions with examples are most welcome (thanks to Rudi Grinberg for contributions so far!).
cheers,
Anil