We use DokuWiki as the collaborative knowledge sharing part of our website http://deprofundis.co.uk/. We chose DokuWiki because it is efficient and easy to use.
One of the reasons I chose Dokuwiki was because of the SearchPattern plugin and the ability to extend this plugin. It has allowed for a very efficient way to annotate information so that it may be easily referenced for users of the site. For example, this simple line1) :
~~SEARCHPATTERN#'/(.Δ]]\s*([^\n\r]+).*)/i'?? -aker:alchemy _sprender ??~~
provides a maintenance free method of annotating any pertinent content throughout the wiki to produce, for example, this reference topic without the contributors having to worry about collating information and ensuring it is up to date.
Please contact me if you have any questions :)