Postman - The Collaboration Platform for API Development
Amazon API Gateway - Create, publish, maintain, monitor, and secure APIs at any scale
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
Paw.cloud - Paw is a REST client for Mac.
Apigee - Intelligent and complete API platform
Django REST framework - Django REST framework is a toolkit for building web APIs.