Postman - The Collaboration Platform for API Development
DataEquity.io - DataEquity: The API Platform for API Governance
Apigee - Intelligent and complete API platform
RapidAPI - API marketplace for finding and connecting to the world's top APIs.
Google Cloud Endpoints - Google Cloud Endpoints provides the tools to develop, deploy, protect and monitor your APIs.
Callcounter.eu - Callcounter gathers API usage data and gives you insight in trends, slow parts and errors.