[jonahx]

Related, and quite good: http://apiary.io/

Apiary not only auto-creates the docs for you, but also auto-creates a mock API which will return the example responses from your docs

[RaphiePS]

Apiary's awesome, but it's great to see open-source alternatives. Every closed-source, lockin-producing service I use is another thing to worry about.

[Almad]

If Apiary would want to lock you in, we'd hardly open-source the parser Iglo is based on and endorse Iglo itself ;)