Yet another RPG subsystem, based on a conversation with Jota, lpsmith, Roger, and others.
The idea here is to work out a system for handling an rpg storyline that has a lot of flashbacks. These flashbacks could be for story reasons ("Ok, all your characters are locked up in jail. So how'd you get here?" "Well, I'd signed on with the crew of this pirate ship, and one day ...") or for explaining why the character has some skill/equipment/relationship not previously mentioned. To make this work, every player picks a couple representatives to use in flashbacks. This could be an archetype ("merchant", "noble"), a place ("the capitol city", "the northern hills"), an organization ("the Crimson Blades"), an environmental condition ("rain") etc.
When somebody declares a flashback, they declare the general setting, and then they're the protagonist and go through the scene as usual. The other players act in the flashback through their archetypes: they can create, destroy, and control instances of their archetypes in the scene just like the GM creates NPCs (so if they declare a merchant, they can set the merchant's bartering skill; if they declare a wall they can set the difficulty to climb it). The object of the scene (for everyone) is for the protagonist to interact with the other players.
Whenever the protagonist interacts with an archetype and is going to make a roll of some kind that relates to the purpose of the flashback (a skill check, a saving throw, whatever), they get a d6. Then they roll all the d6s they've accumulated so far; if the total is at least 15 (or whatever number you set for the scene limit), then the scene is over: instead of making the roll they were about to make, the protagonist narrates the end of the flashback (which probably includes the effect of the roll). If the total of the d6s isn't high enough, then the skill roll goes ahead as normal and the flashback continues. It's possible that when the flashback ends, people get some kind of reward based on how many interactions they had with the protagonist, or perhaps whether they had an interaction or not.