…is now up, incorporating quite a large collection of new material.
There was enough there to convince me, in fact, that I needed a better index — one that would show where facts come from, as well as what they trigger. So the latest conversation graph includes that information. It also shows which conversation topics can trigger the NPC to make a followup comment later. (NPC-directed quips are the ones in square boxes rather than ovals, and they usually have a hyphenated rather than an ordinary name, because their names are never seen by the player. The latter point is just a convention on my part.)
The most recent batches of stuff introduces a few things that might reasonably be called plot developments, and that raises a new challenge: how to maintain continuity when some authors are introducing game-changing events. In one of the strands, it is possible to get Snow White asking you a riddle — which might lead to some sort of stronger alliance with her, I suppose, though I don’t know yet. In another, it is possible to communicate with the spirit of a deceased dwarf and confirm that she is definitely a vampire (at least if you believe what dwarven ghosts tell you). Other strands seem to be suggesting that she isn’t. Yet another points to the possibility of some complicated treason plot involving the true King, who is perhaps not dead, just… out of town?
Emily Short's Interactive Storytelling 
[possible minor Spider and Web spoiler below]
This makes me wonder – are there any examples of games where the players’ actions can change the plot in a non-causal way, from one play-through to another (while remaining internally consistent within each play-through)?
For instance (as above) the outcome of a conversation could shape events which took place before the conversation. There’s nothing to say a game-world has to be internally consistent across play-throughs (though I could imagine it would annoy many players if it wasn’t).
Such an effect could potentially be used to tailor a story to be more satisfying to a particular player. Alternatively, I’m sure there’s lots of neat tricks that could be accomplished with this effect. I suppose this is kind of related to the central mechanic in Spider and Web.
Anyway, I’m finding this whole experiment very interesting, although I’ve only had a couple of quick looks at different versions of the game, and hadn’t had had time to contribute. It seems to be turning from “help flesh out the conversation topics” into full-blown collaborative authorship. Either way, it the mechanics you’ve put together to support this seem to be working really well.
This makes me wonder – are there any examples of games where the players’ actions can change the plot in a non-causal way, from one play-through to another (while remaining internally consistent within each play-through)?
Aisle might count (though it’s not hard for it to remain internally consistent within each play-through given that each is one turn long). Galatea also, perhaps: the different endings give different explanations for what is going on, but it tries up to the endings to be more or less consistent in playing.