This directory contains subdirectories for the various interactive fiction authoring systems. Usually they not only contain the development system, but also a run time system or interpreter that must be used to run the finished (compiled) games.
Jacob Solomon Weinstein announces "raif POOL", a universal language/compiler/runtime/interpreter that can read, write, and run everything you can think of - AI-complete, of course. Just don't believe it; it was an April fool's joke in 1996.