Postman - The Collaboration Platform for API Development
Apigee - Intelligent and complete API platform
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
Django REST framework - Django REST framework is a toolkit for building web APIs.
Amazon API Gateway - Create, publish, maintain, monitor, and secure APIs at any scale
RapidAPI - API marketplace for finding and connecting to the world's top APIs.