I'm really impressed with Stack Exchange's concept of reputation (you gain reputation as you post, and the more you post, the more privileges you get), and I want to apply the concept to a wiki that I am building.

Does anyone know of a php wiki that has a concept of privileges/reputation similar to Stack Exchange? I'm not necessarily looking for something identical to SE, I'm just looking for a wiki application that gives users more privileges the more they contribute positively to the wiki (SE has down votes, the wiki should have some way of identifying negative contributions too). The privileges should be category based, so the more active you are in a specific category or page, the more privileges you get for that category. There should also be site wide privileges as well, though those should be harder to access than the category privileges.

NOTE: If it is not possible to get category wide privileges and site wide privileges, I will be OK with just category wide privileges or just site wide privileges.

I should be able to change the requirements for each privilege, through a administration panel or through editing a file (some wiki applications don't have administration interfaces).

Does anyone have a script or a solution that will do this? If the script uses something similar to reputation to determine how much a user has positively contributed to the site, then that is OK too.

Please Note: I am looking for a way to rate individual user contributions, not a way to rate the quality of an entire page.