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

Voiden is a developer-first API client with local storage, Git-integrated, all based on markdown + offline support.

Browser and Mobile Automation Test Framework for Node.js

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

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