I was investigating the same question recently myself. This is what I came up with.
The best support for TeX input to my knowledge has Noösphere which is the engine behind PlanetMath
I however do not believe that you can install Noösphere on your own-servers because it is proprietary application. Please somebody correct me if I am wrong.
On the another hand I really like PmWiki
which also has support for TeX input.
There is another feature of PmWiki that I really like. You can store your date in plain text files. Most but not all Wikis do require some kind of database.