TiddlyWiki is a Wiki system implemented completely in JavaScript. The whole Wiki plus the script is contained in a single HTML file, so that it is very easily distributed. No need for anything server-side, or even for a server at all (you could put it on a disk or send it around by email). It is also surprisingly feature-rich: You can edit the content right in the web browser, save the updated file to disk (requires IE or Firefox, but support for other browsers is planned), you get the usual text formatting tricks, there is support for using it to run a weblog (including creation of an RSS feed), and even a built-in search engine, a user-extensible macro system, animations, a timeline and tags.