Ask HN: What tools to use for Api First Development?

I read this site http://www.api-first.com/

and it makes a lot of sense. If we were to have an API backend that would decouple it from front facing applications such as web application, android, iOS app, which would simply make a call out to the API backend.

This would avoid having us to rewrite and redo the work over and over again in different languages, different client SDKs, frameworks etc.

What are some good software tools/libraries that let's you build CRUD, authentication, around existing databases?