[Haskell-cafe] Writing tool question (may be out of scope here)

Hi, Excuse me if that is out of subject here, but does anyone know which tool/writing framework was used to write the "Real world Haskell" book ? I'm wondering, in particular, about the capability to write/edit/publish it online while allowing people to leave comments, then have a paperback/PDF version. Thanks in advance, -- Saul