Friki is a small, fast, flexible open-source wiki written in Java and easily deployed by simply dropping a war file into any standards-compliant Java servlet container or application server. Note particularly that Friki does not use Java Server Pages (JSP) and will run quite happily on a server without a Java compiler.
Friki is extremely configurable, most things (including page style and markup syntax) can be changed without restarting the server or the application or recompiling any code. The application can also be easily extended with user-written plugin classes which will be automatically loaded as required.