Tabletop roleplaying games (TTRPGs) are set apart from other interactive artforms by the core assumption that their game worlds and game systems can change even during play. This quality, which I call malleability, underpins free choice of action by players, and runtime redesign by Game Masters (GMs.) Despite the importance of this unique quality, on the eve of TTRPGs’ 50th anniversary, there are still no computer adaptations of the medium which both retain full malleability, and make meaningful use of modern computers’ processing power.

Computer roleplaying games (CRPGs) use modern computers’ storage andprocessing capabilities to present large worlds and deep gameplay mechanics, while keeping large amounts of information manageable with slick interfaces and audio-visual feedback. However, because they are completely mediated by the computer, they give up all malleability.

Virtual tabletops (VTTs) offer somewhat more malleability than CRPGs byonly partially mediating gameplay. Nevertheless, much of what would be malleable in traditional play is static during VTT play. Furthermore, because VTTs focus on faithfully recreating game systems and accessories which evolved in an analog context, their gains from existing as software are mainly limited to networked play and improved graphics.

In this thesis, I present a novel software system which supports complex game-play mechanics and information-rich user interfaces, while also offering malleability of a game’s rules and world at runtime. As part of my justification for developing this system, I give the first comprehensive account of malleability and its importance to the design and play of TTRPGs, and I propose and defend a novel method for quantitatively analyzing the complexity of TTRPG systems.