Here is a list of all documented files with brief descriptions:

src
libprimis-headers
command.h	Script binding functionality
consts.h	Useful egnine constants
cube.h	Needed for making games, along with iengine.h
ents.h	Static map entities and dynamic entities
geom.h	Physical geometry objects
iengine.h	The interface the game uses to access the engine
octa.h	Objects representing the octree and its manipulation methods
prop.h	Type-agnotic property system
slot.h	Texture slot objects
sound.h	The sound engine that translates world positions into positonal sound
tools.h	Legacy tooling inherited from the Cube engine