...over the weekend.
It has a couple of features that made it perfect for a vague idea I had... specifically, it has a permissions system, so you can make pages and sets of pages read and/or write restricted. I know it's counter to the "WikiCulture", but that's what I wanted - because my idea was to offer wiki-space to people who couldn't install their own so they could sort out their story background out, but I certainly didn't want just anybody reading my story background! So there's public areas and private areas. Basically I wanted it for the easy page creation and cross-referencing, not the collaboration.
By the way, what kind of organisation are you using for your story background? I've got index pages for character, settings, culture, and history, then the details are all in a tangl^H^H^H^H^Hnicely cross-referenced web of pages. I'm kind of curious to know what you did, because I'd like to have a good organisation system. I like being organised...