A bit of a preamble for anyone not familiar with the acronym – there’s a movement or set of movements known as the FKR, standing for Free Kriegsspiel Revolution, a (mostly) joke term intended to contrast with the OSR to focus purely on a relationship to rules in gaming – namely that the referee is the interface between the fictional world and the player characters.
These movements tend to primarily focus on very small rulesets – often stuff like “d6 roll for low” or contested 2d6 rolls, just because these kinds of rulesets allow the referee to really focus in on rulings. I think there’s also a bit of fondness for how Bob Meyer runs Blackmoor.
So from the outside lots of people are starting to assume the FKR means nearly no-rules roleplaying games. But if you look at Kriegsspiel itself, or even the kind of rulesets Arneson seemed fond of writing – sometimes there are a lot of rules. And this to me is an important thing to note. It’s not the amount of rules.
FKR to me is purely a relationship to rules. If your table is composed of a referee who portrays the world opting to use rules as a tool whenever they wish, and players portraying characters responding with what they would do if they were in whatever fictional situation the ref is describing – that to me is FKR. It doesn’t matter if the ref is using a single coin flip, or if they decide to sometimes opt into Mythras, or their own hack of ASL, or anything else. The amount of crunch doesn’t impact the FKRishness, its if the table is focusing more on the fiction over the mechanics. This is obviously easier with light systems, but if the ref feels using something heftier “behind the screen”, that’s a perfectly valid approach.
That’s just me though.