Postman - The Collaboration Platform for API Development
Freshservice - Freshservice: the one-stop cloud solution for all your IT management needs.
Amazon API Gateway - Create, publish, maintain, monitor, and secure APIs at any scale
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.