Postman - The Collaboration Platform for API Development
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
Gravitee.io - Gravitee.io is a flexible, lightweight and an open source API management solution.
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
Apigee - Intelligent and complete API platform