A system for writing interactive fiction that models the discourse and dialogue as well as the world in such a way that it can drift slowly over time (i.e., as players interact with it). Allows for different narrative systems (flashbacks, intercutting, out of order). Requires some knowledge of narrative theory, IF, and python to really use. Useful to people researching computational intelligence and development systems. Seems like it's for use on top of other text-based systems instead of implementing a full one.
William Gibson's self-destructing work Agrippa has been reconstructed from one of the original diskettes (it was never actually released) and put online as a simulation.