Torchbearer has many rules that I think could profitably be spliced into more traditional dungeon crawling games. Of these, light coverage is perhaps one of the easiest to apply. Light coverage is the idea that the amount of illumination provided by a given light source is limited. Rather than trying to measure this using a literal approach of light radii as is commonly done in D&D, Torchbearer measures illumination by the number of characters that can benefit from a given light source (1 for candles, 2 for torches, and 3 for lanterns).
In addition to the number of characters fully covered by a source of illumination, a similar number of characters are in dim light. For example, a party of seven adventurers with one torch would have three characters in full light, three characters in dim light, and one character in darkness. Both dim light and darkness are factors in Torchbearer tests, which could easily be modeled as situational penalties in other games. The exact numbers here do not really matter, and could be adjusted to reflect however various light sources are conceptualized.
While considering how to handle grenades or other area affect attacks within a monologic combat framework*, Gus suggested that perhaps various area affect attacks, such as grenades or fireballs, could have an explosion rating indicating the maximum number of enemies that could be affected. I immediately thought of light coverage. Splash or blast damage, like movement distances, are hard to resolve satisfactorily and without handwaving when using fictional positioning. In the past, I have thought of area affect
The coverage rating would reflect the most targets that could potentially be affected by a given effect or item. The referee would still need to make a ruling about whether or not this coverage capacity was “filled up,” but the coverage rating would provide convenient and easy to understand guidelines, along with an upper bound. A second tier of effects, similar to how Torchbearer handles dim light, could be used to model something like secondary splash damage from a molotov cocktail. Coverage ratings could also be used for weapons such as nets, or even potentially special attacks using more conventional weapons (two-handed sword sweeps and missile volleys come to mind).
I suspect this general coverage approach could also be applied to abstracting other rules that are difficult to get a clear shared geometric understanding about.
* See: monologic combat.