This system of roleplaying is where players are responsible for their own advancement in the game. In essence, they cannot depend upon the Game Master to move them forward, as the Game Master's task will be to ensure players follow the rules and develope the plot only when players reach a certain level of the gameboard.
Like peices on a board game, players have a initial starting position. (Depending on the game this can be the same location or different locations)These initial positions can be determined by the players choosing, GM guidance or a cooperative agreement between the two. Throughout the board there are spots to where players can access a 'card', persay, from the drawing pile and either experience a push forward or a set back. The cards include:
"Move Six Paces Forward": As players start off in an initial position (intitial thread in this context), getting this card means that the players have come to a certain place in the game that allows them to move forward to other threads.
"Move Six Paces Back": As players move throughout they threads they can come into conflict and draw this card which sends them back to a previous thread (most likely the original starting thread if the game is setup like that), or make them have to back track their movements to find someone or something that they've encountered before be it a Monster, Player or NPC.
"You've found a Special Item": Along their movement toward the goal of the game, players can draw this card which equips the player with soemthing that advances them in the plot. (A power up, Plot infomation etc.) These cards can also help them to advance far into the story before anyone else.
"Go to Jail": Drawing this card is some serious bad luck, because this mean that a character has been put in a place of immobility and must wait for someone else to come save them. (Getting captured, thrown in a dungeon or being seriously injured.)
Which 'card' you have is determined by a number of key factors:
Move Forward: This card is determined by character interaction. A player can only advance to another thread when they have interacted with another player. The more threads a player moves through, the more interaction they must have.
Move Back: This card is determined by a enviroment. If you come to a conflict that you don't know how to solve you must back track (like a locked door or a monster you can't defeat). If your character meets a character who asks you for help you must back track, if you accept. If you need something to defend or get you an plot advancement, you must back track.
Special Item: This card is usually given by the Game Master and can come in the form of an informational NPC or even a gift from another character (though the gift can be given from the GM or as an revealed something from the player's character's past.) These are only given when you've reached far enough into the game. They can be things like a weapon or a power.
Jail: This card is also given by Game Master, or by a character. If a player decides to be a villian or perhaps there is a misunderstanding between two characters would be some of the circumstances that allow this. Of course, it's all okayed with the players involved and GM.
The job of the system is to make players interact and ask for aid from other players. While players can have different stories, the stories intertwine to the heart of the plot. It helps for the players to have to rely on each other and develop the story that way. This system works best when the players have characters whose histories tie into the story and have purposes to reveal the story.