MockServer - Easy mocking of any system you integrate with via HTTP or HTTPS.

Mockable - Quickly define some REST or SOAP endpoints and have them return json/xml (dummy) data.

Beeceptor - Unblock yourself from API dependencies, and build & integrate with APIs fast. Beeceptor helps you build a mock Rest API in a few seconds.

RequestBin - RequestBin.com gives you a URL that collects requests you send to it so you can inspect them in a...

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.

HttpMaster - HttpMaster is a professional software tool for testing and debugging HTTP applications, primarily aimed at REST API applications and web services.