sfall's main configuration options appear in ddraw.ini, but there are several other configuration files that it can read in for modding purposes.

Books.ini: Lets you override/add books to the game (associated object PIDs, skills and text messages)
Perks.ini: Lets you override the name/description/frm image/other stats of perks and traits
Elevators.ini: Lets you override which elevators lead where
CriticalOverrides.ini: Lets you make modifications to the critical hit tables
Translations.ini: Contains some text strings which sfall displays, to allow their translation
Skills.ini: Lets you change the formula used for calculating skills
Stats.ini: Lets you change the formula used to calculate the derived stats