There is grape, grape-swagger, grape-swagger rails, and a bunch of other gems for creating API's. They work amazingly well, and have a pretty active community.

There is grape, grape-swagger, grape-swagger rails, and a bunch of other gems for creating API's. They work amazingly well, and have a pretty active community. They have solved a ton of issues: Jsonp, Cors, authentication, rate limiting, versioning, and DOCUMENTATION. The auto-generated Swagger documentation is a real thing of beauty.