WikiJet 0.2 is a wiki codebase that supports lib-user logins (and restricts edits to logged-in users), page histories, reversion to old versions, recent changes (no RSS yet), a complete list of pages, and Markdown syntax.
Wikilink text by surrounding it with double square brackets. (There may still be some issues with the way it normalizes the text to a page title.) To make a new page, make a link to a page first. Then follow the link and fill in the blank page that you land on. Or just type some stuff into the URL and hit a new page that way.
For everything else that goes on a page: Markdown syntax. HTML will be stripped.
View the source for the rest, and clone away (consider it GPL). Have fun!
Note: there is lots of stuff in Markdown syntax. Like code blocks:
function haxor() {
print(OMG(WTF()));
}