Postman - The Collaboration Platform for API Development
Google App Engine - A powerful platform to build web and mobile apps that scale automatically.
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
Dokku - Docker powered mini-Heroku in around 100 lines of Bash
Paw.cloud - Paw is a REST client for Mac.
Google Cloud Functions - A serverless platform for building event-based microservices.