Shameless plug: for REST APIs, I've written a tool called Instaunit which combines HTTP API integration tests with documentation generation, since these two things must always be maintained in lockstep.
It's got a ways to go before it generates output that looks as good as Stripe's documentation, but it makes it dead simple to create API documentation that's guaranteed to be in sync with your service, because it was generated by your tests when they ran.
The documentation does not seem to have any examples of the generated docs, though. I think that would be a good addition, because it’s a good selling point for the project.
(I.e I don’t think I’d go through downloading and running it just to see if the generated documentation is ”good enough”.)
It's got a ways to go before it generates output that looks as good as Stripe's documentation, but it makes it dead simple to create API documentation that's guaranteed to be in sync with your service, because it was generated by your tests when they ran.
https://github.com/instaunit/instaunit