Everyone wants “hello world” application for being convinced, that the thing can work. Here is one written in Haskell and web-related. It’s quite straight-forward:

import Network.FastCGI
import Text.XHtml

htmlPage
  = header
    << thetitle
      << "Hello World!"
  +++ body ! [ bgcolor "white"] << "Hi"

main = runFastCGIorCGI (output (renderHtml htmlPage))

To make it working, you need GHC and fastcgi library (with all it’s dependencies)