This Saturday morning, my mission was to decide on a wiki to use for my website. I need to do some things like tracking progress and information related to projects for my clients (setting up a new business). I have worked with a few different wikis, none of which is exactly right for me (Confluence costs money, TikiWiki is too bloated, and most don't support the kind of access control I need).
With some help from http://c2.com, I decided (so far) on PmWiki. I'm just getting into it, but PmWiki looks fairly simple and lightweight, but like it will support what I need. (user authentication, namespaces with ACLs of some kind, skins, etc.). The custom markup feature looks very cool too - simple but very flexible.
Maybe I'll contribute a little to this project if it becomes a central part of my website and workflow. We'll see...