Request inspector - Debug web hooks, http clients
Mockable - Quickly define some REST or SOAP endpoints and have them return json/xml (dummy) data.
MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.
Postman - The Collaboration Platform for API Development
CurlHub.io - API Traffic Inspector
Webhook.site - Instantly generate a free, unique URL and email address to test, inspect, and automate (with a visual workflow editor and scripts) incoming HTTP requests and emails.