Anatomy and physiology, health, damage, poison, and regeneration.
Astronomical sciences, from the galaxy to the moon.
Biological, taxonomy and similar subjects.
The Book of the Game, I guess.
Thinking and decision-making.
"Text" shouldn't mean "ugly".
Combat system, some closely related topics.
Debugging tools, macros, etc.
Parsing, tokenizing, etc user input.
The world in which things happen.
Economic system, merchants, resources, scarcity.
Sensation and perception of the environment.
Geology and physical geography.
Everythiiiiiiiiiiiiiiing...
Goal-Oriented Action Planning
Infrastructure to help me do the things.
Linguistics system permitting communication, bidirectional translation, etc.
Narrative/mythopoetic procedural content generation and tools.
Rooms and navigation between them
Embedded programming language and domain-specific library.
Social psychology and sociology, individual and group behavior.
Supernatural and metaphysical concepts, the thermodynamics of spirit.
Tool for humanizing numbers, concepts, etc. Syntactic sugar.
Anything related to automated testing.
Frontend and connective logic. As little as possible.
Our representation of the world through which we actually move.