TiddlyWiki to the power of App Engine
If you think TiddlyWiki is wonderful, except that it isn't a real wiki in the classic sense, this could be the wiki engine for you. giewiki tries to be a real wiki: You get preview and versioning of tiddlers, any number of pages in any hierarchy, auto-generated sitemap, full-text search, comments on tiddlers, fine-grained access control, image upload, recent changes, etc.