Ask HN: Models for Collaborative Websites?

I am playing with the idea of creating a niche information website, where I want users to be able to contribute and improve the content.

I am looking at the Wikipedia and StackOverflow models to get inspiration on how to foster quality contributions. Is there any other good example of a website where good quality content emerges from user contributions?

Using a pure Wiki or Stack-exchange model is not an option, because:

- I want to be able to impose a schema for the different items that can be documented, to improve searchability, so a wiki is a bit too unstructured, but

- the general structure should be closer to an encyclopedia than a Q&A

The aim is to provide a collection of quality information, which is missing in that niche, not to make money, in case that matters.