I’ve seen various versions of TiddlyWiki around the internet, all of them interesting. What caught my eye about this one is the data format. RSS is used for versioning and data storage. You can of course subscribe to the same feed to track changes. Very interesting use. It currently uses RSS 2.0 though I’m sure it could be changed to the format of your choice if you wanted to.
TiddlyWikiRemote - a wiki for your laptop