RSS Box : This app uses the API of other websites and gives you an RSS feed in return. Quick and simple.
JSON Schema : JSON Schema is a vocabulary that allows you to annotate and validate JSON documents.
Gluon API : A clear, concise, simple yet powerful and efficient API for deep learning.
Swagger : Swagger is a powerful open source framework backed by a large ecosystem of tools that helps you design, build, document, and consume your RESTful APIs...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Bluepine is a DSL for defining API Schema/Endpoint with the capabilities to generate Open API (v3) spec, validate API request and serialize object for API response based on single schema definition.