A fascinating paper from 1990 describing the game 'Habitat', a pre-Internet progenitor of the MMORPG genre. I particularly like how the authors distinguish between the infrastructure level and the experiential level of the game and the emphasis on the importance of the sociological and economics-oriented aspects of the system: what I would call the soft technologies of the game. Though some of the technical issues seem quaint and dated, most if not all of the lessons and principles are as relevant to social systems design today as when the paper was written.