Just had this though half an hour ago, so it's extremely raw. The idea is a game of dark but somewhat pulpish conspiracy.
Setting: there exists Project Dreamland. This fact is the only solid truth in the game.
In the game each player has a pool of "rumour points", for lack of a better name. A player may spend a certain number of these rumour points in order to create a rumour (I guess the number of points needed to be spent depends on the rumour). The rumour is said in the open (everybody knows it exists), it is written on a piece of paper and is put in the "rumour bowl".
At some points during the game the GM pulls out a rumour at random. He doesn't tell the players which rumour this is - but it is from this moment on solid truth in the world (of course, the GM should be honest about this).

Result: there are lots of rumours going around, but the players don't exactly know which of those are true and which are false. This also gives the players certain narrative control of the game, and allows them to push the game into new directions.

Examples:
1) The player starts a rumour: "early non-successful results of Project Dreamland caused strange mutations in the subjects. Some of those have escaped and now live in the Sewers beneath the city". Later in the game, the players face the decision of going down to the sewers. Are there mutants down there? Perhaps. Maybe the GM has pulled out this rumour already. Maybe not.
2) The players have been to Area 51 and saw some of the horrible experiments that took place there. When they exit, one of the players starts the following rumour: "Area 51 doesn't actually exist. It's a hoax". If this rumour becomes truth... where have they been, then? Was it an illusion? A masterfully constructed red herring? And who stands behind it?

Some thoughts and ideas:
1) How do players refresh rumour points?
2) How much rumours do we want in the game at any given moment?
3) When does the GM pull out rumours? When he feels like it? At certain defined points (at the beginning of a session, every hour, at critical plot points)? Can the players force him to pull out a rumour, say, by paying a certain number of rumour points?
4) What, exactly, are the scales of things, how much do various rumours cost?
5) Can the players do other things with rumour points? Forcing the GM to draw a rumour like I've said above, perhaps. Perhaps they can pay so that the GM reveals one rumour which is currently true. Another option: instead of starting a rumour, players can pay more (say, twice a much as that rumour would have cost normally), and instead of starting a rumour, they simply state a fact (it becomes truth).
6) What if the GM has his own pool of rumour points?

Your thoughts?

OK, so lets seee what we have here:

1) How do players refresh rumour points?
I'm thinking it would be scene based or maybe if its a sort of flowing time, then a time based reset?

2) How much rumours do we want in the game at any given moment?
Enough that its uncertain which are true, but not so many its hard to keep track of. Rumors I think might come and go, with a limit of maybe 2 or 3 for every player at a time. Maybe when the limit goes over, some come true?

3) When does the GM pull out rumours? When he feels like it? At certain defined points (at the beginning of a session, every hour, at critical plot points)?
I'm thinking every time unit, or maybe every scene would be good.

Can the players force him to pull out a rumour, say, by paying a certain number of rumour points?
I like this idea.

4) What, exactly, are the scales of things, how much do various rumours cost?
I don't see why any rumors would cost more, although you might want to set up some ground rules- like in wushu where you can narrate anything except an auto-kill, etc. I mean sure players could do something crazy, but that's kind of the point isn't it?

5) Can the players do other things with rumour points? Forcing the GM to draw a rumour like I've said above, perhaps. Perhaps they can pay so that the GM reveals one rumour which is currently true. Another option: instead of starting a rumour, players can pay more (say, twice a much as that rumour would have cost normally), and instead of starting a rumour, they simply state a fact (it becomes truth).
I think they should definitely be able to spend them, but I don't think they should be able to just declare facts, as I think that might just ruin the mood. However, I can see revealing facts to be an interesting idea, although maybe make it tied to an in game scene where they find out the fact, or make it harder by having them just pick an rumor and asking whether its true or false, and charging them every time they do that, and make it expensive.

6) What if the GM has his own pool of rumour points?
This could work well, although if the GM is the final interpreter of events and the weaver of the story then I'm not sure if they'd need them.

Hope that helped. Cool idea!

Hey, Oddin!

I'm intrigued by your idea - it reminds me of those lists of rumors in Unknown Armies - endless story seeds! But here, well, they aren't just story seeds; they're already plot elements! Awesome.

I think that the rumor mill would need a couple of guidelines, depending on the time frame of the story - for shorter tales, over the span of a few days, I think a new rumor every two or three scenes (or 1-2, depending on how many there are...) would work, whereas a larger conspiracy-tale over several months might require that you only have one once each session, or suchlike.

Now onto my questions/thoughts for expanding the concept:
1) Who are the PCs? What's their role in all this? How do they related to Project Dreamland?
2) I'm envisioning it as a sort of one-shot, one-storyline deal: once you discover (well, determine) the mystery of  Project Dreamland, you're done. Thoughts on this? Maybe that's not at all how you envision the plot structure, though.
3) Are there going to be agreed-upon constraints on rumors, based on theme, mood, and even maybe a character sheet question "Why are you so drawn to Project Dreamland?" that the player answers on behalf of his character? I think doing stuff like that would keep it from erratically changing mood, and maybe provide a more graceful transition as each rumor is made Truth.
4) Is this game about winning? About enjoying the weirdness? Or what?

Cool stuff. I'm eager to find out more!
-- Abby