Mockoon is the easiest and quickest way to design and run mock REST APIs.

Hand-crafted lightweight Rest Client for testing APIs. Supports collections, environments, git collaboration and local storage.

A modern, resource-friendly REST client for Windows 10

Charles is a HTTP proxy that enables you to see traffic between your machine and the backend

A browser extension and Ruby gem to improve the debugging experience when testing Rails applications

Built for developers and testers alike, SoapUI is the only open source tool that covers the entire testing spectrum (functional, security, load, mocking).