There are a lot of rules systems, debates over the extent to which system matters, and groupings of rules into groups. Based on advanced paleontology, historico-linguistic comparative analysis, and the latest genetic evidence, I have cloned the most basic systems to display them in this post, my personal Jurassic Park.
Primordial Sim
Players describe what their characters do, and the GM decides what the likely outcomes will be. If it's not obvious whether it would succeed or fail, she flips a coin.
FKR isn't about the amount of rules, but one can read a lot of FKR-style play as essentially this, with optional bells and whistles. Indeed, I think the core claim of FKR is that all other rules in a game can be considered a sort of midrash which advises the execution of Primordial Sim.
Hadean Narrativism
A storyteller tells a story.
You might say that this isn't a game; that's quite true, in fact ludochemists have reconstructed it from processes they believe to have begun during the Hadean Eon, before there were games proper, but as certain molecules were beginning to behave in a game-like way.
Archean Narrativism
Players describe what their characters do, and the GM decides what would make for the best story. If it's not obvious, she flips a coin.
During the Archean Eon, the primordial soup began to bubble, and Hadean Narrativism evolved into a game-form. It is most well-known for two descendants.
Primordial Narrativism
Players take turns telling a story.
Primordial Illusionism
Play Archean Narrativism, but say you're playing Primordial Sim.
Thus we have three basic primordial body plans - PS, PN, and PI - that describe the rules of all roleplaying games.
IMO, species-level system differences do not matter that much, especially within PS/PI, but phylum-level differences do.
