Community-Driven Documentation for Free Software?

const_k asks: "I'm maintaining TightVNC, a popular free software project. As with many other free and open source projects, there is a problem with having comprehensive documentation. Currently, I'm thinking about launching a sort of community-driven documentation project, using Wiki as an engine that would help volunteer contributors to write and improve the documentation. I'd like to know, is it a good idea to use Wiki, and is it possible to achieve decent documentation quality this way? What software and technologies other free or open source software projects use, and what are the results, in terms of completeness and quality of the documentation? Any pointers and suggestions would be greatly appreciated."