What's an advisable way of documenting and sharing APIs (e.g. HTTP web-services)?

The requirements are:

* A Wiki type system in which anyone can edit any page.
* An easy way to write an API spec so that the styling/formatting is applied automatically, rather than having to manually add the styling for each individual page.

I would use [Wordpress](http://www.wordpress.com), except that it's not really a Wiki system; it's more of a blog engine. I want a nice, clean, structured hierarchy of pages, and the ability to **click and edit** instantly.

I tried [Google Sites](http://sites.google.com), but this also seems to be unsuitable, because it doesn't allow me to create a consistent style for APIs. The only control I have over styling is "themes", which change the look & feel of the whole site, and aren't specific enough.

I found a [hosted solution here](http://pbworks.com/content/API+Documentation?_kk=api%20documentation&_kt=fd785e1d-5b5b-4f2c-8c80-0db860205c9a), but at $499 p/year I'm sure we can do better.

Any suggestions?