Storyboard
This is a new idea that I just came up with and want to look into prototyping this feature.
How it works is that you have a list of characters plotted on the Y axis and events/time plotted on the X axis.
Each character is graphed with a 'path' along the X axis that can go up or down depending on the other characters that are involved with a particular event.
I don't know the name of this (graph?) but I'll sketch up an example soon.
But basically this tool can be used for authors to structure out their stories if they want to. Think of it as a complimentary feature.
For each of these characters in the story, you can click on them and provide details about these characters that are only accessible by authors for their own internal use (not publically available for spoilers).
I'm not sure how far this could go, but as soon as the critical features are sorted, this is something to jump into and start prototyping.