This page is an attempt to explain a particular collection of roleplaying techniques known as "No Myth". It's not something I made up — it's by this guy on the Forge, Le Joueur (there are links to the Forge and stuff at the bottom of this page) — but it's a style I am interested in trying seriously myself, so I've put this page together. Thus:
The premise, and the reason it's called No Myth, is this: nothing you haven't said to the group exists. "You", in this case, includes the GM as well as the other players. The other half of this premise is "the [non-GM] players are the protagonists of the story." The result of this is that if the characters are mob enforcers and they go into a bar, something cool happens. Maybe they see the stoolie they're looking for in there, maybe there's an ambush in the bar by a rival mob, maybe the bartender's looking nervous because it turns out he's in default on his "loan". Whatever — the point is, there's something cool as a result of their action, because the goal of the system is for the GM to facilitate cool stuff happening.
Note that this is not saying that the players get to say what happens when they go into the bar — the story is still being "run" by the GM — nor is it saying that player actions are meaningless or that their effects are arbitrarily decided by the GM — the effects are directly based on genre, the characters' previous actions, and what would be cool to have happen.
The overall goal here is pretty simple: make more cool stuff happen per unit time. This system (at least in theory) facilitates that, with the cost that it relies on having a clear understanding of the genre you're working in. That means two things: they have to understand the common elements of the genre, and they have to understand the rules by which they interact. For instance, a game where the PCs are mob enforcers probably has elements like scenes in Italian restaurants and barbershops, car chases, stick-ups, double-crosses, a suitcase full of cash or gold bars, leg-breaking, protection money, gambling, and the old don saying "Listen, Vinnie, the boys want to have a little talk with you". But along with the elements, the players have to know the rules of the world. If things get to the point where the don says that to you, you're probably going to die. If the player is envisioning more of a heroic swashbuckly game, they might say "Well, I drop down suddenly and roll across the floor, firing shots at the don's bodyguard to keep them back until I make it to the door." — only to be disappointed if the GM says that's not particularly realistic, applies heavy penalties to the roll and the bodyguard shoots the PC as they're still trying to get their pistol from its holster.
For another example, if the PCs are at the edge of a cliff with the bad guys closing in, they need to know what's likely to happen if they jump off. Can PCs die if they do something stupid, or (assuming jumping off a cliff is stupid) would they fall onto some branches partway up? Or would they be rescued by a friendly hermit at the bottom of the cliff after they land, having broken a bunch of bones in the fall, and be laid up for months? Or (if we're talking something more nobilis-level) do they land on their feet at the bottom and keep on running? To take another example, if the players had gotten captured by the bad guys, would the bad guys kill them? Or would they tell the PCs their secret plan and then put them into some kind of crazy death trap? Is it reasonable for a player to create an anti-hero PC? Or are they all supposed to be basically good guys? If the party splits up, do they get picked off one by one, or do they search the spooky mansion faster that way? Are PCs basically witty and talkative, so the combat-heavy mercenary is an unpleasant thug, or are they special-forces agents and the one diplomat is a dangerous liability?
I don't think all the rules and elements need to be ironed out, but without at least a basic premise being agreed upon, there's going to be confusion. Because of this, No Myth works better with strongly defined genres. "SF", say, would be a lousy setting since you don't know if there's AI and how powerful it is, whether there's nanotech, if FTL exists, and so on. "Star Trek", on the other hand, answers all those questions, and also includes a sense of who the characters are, what sorts of things they do, what the overall morality/philosophy of the universe is, and so on. I think that people make movies or write adventure books about are well-suited for this kind of game: pirates, musketeers, superheroes, Westerns, mobsters, sword and sorcery, Robin Hood, heist caper, Star Wars, that sort of thing (although many of these genres require pinning things down more before you start — do you want your Western to be "We got to get the cattle to Sun Valley by May!" or "You left me for dead, Black Pete, and now I'm back for blood").
I think No Myth would work well with a pretty large set of mechanics. The FUDGE variant I was working on seems like an obvious fairly free-form choice, but this could work just as well with a Nobilis or 7th Sea or even d20 adaptation, depending on the genre (d20 is probably more detailed than is ideal, but I imagine you could strip it down). I think the important thing would be working out the procedure for setting stakes and goals and deciding their scope, and also working out what the right chance of success should be. I don't know this for sure but my gut feel is that for maximum interest, players should succeed on most tasks 40-80% of the time. Outside that range, outcomes become predictable, which makes the goals less significant. These numbers are lower than what's normal in some cases, but I think the fact that players succeed when it's not interesting for them to fail will compensate for this in terms of overall feeling of accomplishment. In addition, when they do roll, failure leads to something interesting, so the players aren't losing anything by failing.
Finally, some links about No Myth, mostly to threads on The Forge by Le Joueur, the guy who invented No Myth (if you're reading posts on The Forge for the first time, the glossary would probably be helpful to look at):
And that's the wrap. Lemme know if you have comments or want clarification or are interested in playing in something like this.