Whilst Wiki markup language can be a little intimidating for the novice user it is hard to argue with the overall success of the Wiki concept especially when you take a look at sites like Wikipedia. I have tried a number of Wiki tools but DocuWiki is my favourite for a number of reasons.
Firstly it just seems to work with very little hassle, mainly because it is written in PHP and does not rely on any back-end database, preferring instead to save all data to files on the disk. I also like it because it gets up and running without any major configuration process, if you have the correct PHP extensions loaded and file permissions set it will just work with almost no questions asked. To top it all off if the extensive built in functionality does not meet your needs it can be easily extended through the use of plug-ins as this Linux.com article illustrates.