"Version 1.5 of this powerful wiki is readily available for easy installation in Ubuntu 6.04. Some of the major new features of MoinMoin 1.5 include a GUI wiki page editor and the ability to render a wiki page as DocBook XML."
Gobby is a free collaborative editor based on libobby, a library which provides synced document buffers. It supports multiple documents in one session and a multi-user chat. It runs on Microsoft Windows, Mac OS X, Linux and other Unix-like platforms.