Beeceptor - Build a mock Rest API endpoint in seconds.
WireMock - WireMock - a web service test double for all occasions.
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.
Postman - The Collaboration Platform for API Development
RequestWatch - Inspect and debug HTTP requests
Mockable - Quickly define some REST or SOAP endpoints and have them return json/xml (dummy) data.