5) The OSR ("Old School Renaissance / Revival")
Yes, it's this late in this chronological listing. And yes, the OSR is not "classic" play. It's a romantic reinvention, not an unbroken chain of tradition.
The OSR draws on the challenge-based gameplay from the proto-culture of D&D and combines it with an interest in PC agency, particularly in the form of decision-making. The goal is a game where PC decision-making, especially diegetic decision-making, is the driver of play. I think you can see this in a very pure form in
the advice Chris McDowall gives out on his blog for running Into the Odd and Electric Bastionland.
An important note I will make here is to distinguish the progressive challenge-based play of the "classic" culture from the more variable challenge-based play of the OSR. The OSR mostly doesn't care about "fairness" in the context of "game balance" (Gygax did). The variation in player agency across a series of decisions is far more interesting to most OSR players than it is to classic players.
The OSR specifically refuses the authoritative mediation of a pre-existing rules structure in order to encourage diegetic interactions using what S. John Ross would call
"ephemeral resources" and
"invisible rulebooks", and that the OSR calls
"playing the world" and
"player skill", respectively. Basically, by not being bound by the rules, you can play with a wider space of resources that contribute to framing differences in PC agency in potentially very precise and finely graded ways, and this allows you to throw a wider variety of challenges at players for them to overcome. I could write an entire post on just what random tables are meant to do, but they tie into the variance in agency and introduce surprise and unpredictability, ensuring that agency does vary over time.
I tend to date the start of the OSR from shortly after the publication of
OSRIC (2006), which blew open the ability to use the OGL to republish the mechanics of old, pre-3.x D&D. With this new option, you had people who mainly wanted to revive AD&D 1e as a living game, and people who wanted to use old rule-sets as a springboard for their own creations. 2007 brought
Labyrinth Lord, and the avalanche followed thereafter. The early OSR had
Grognardia to provide it with a reconstructed vision of the past to position itself as the inheritors of, it had distinct intellectual developments like
"Melan diagrams" of dungeons and Chris Kutalik's
pointcrawls, and I would say it spent the time between 2006 and roughly 2012 forming its norms into a relatively self-consistent body of ideas about proper play.