I have found one of the best .NET Wikis on the net, it is Screwturn Wiki, the creator of this wiki engine has developed it in C# using .NET 2.0. t does not need a database and has a large portion of wiki benefits.
I needed to use a wiki for in-house documentation and interactive discussion on the development of a manufacturing production recording system. One of the biggest problems with projects of this type is that all of the principle players work different shifts and days. With a wiki I can get and respond to any concerns, comments, suggestions, or criticism in a short period of time.
This wiki has an easy to install web install package, it also has a desktop edition that will install without IIS on your computer.
If you are looking for a open source wiki with a majority of bells and whistles that you would find in a enterprise (cost a bucket load of money) solution, then check this out, you will not be disappointed.