Robot Framework is a generic open source automation framework. It can be used for test automation and robotic process automation (RPA).

API Testing Platform that automatically generates unit test cases with dependency mocks from API calls

Puppeteer is a Node.js library which provides a high-level API to control Chrome/Chromium over the DevTools Protocol.

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

Simulate APIs, integrations, and environments at enterprise scale.

Free & OpenSource REST API Testing Tool for all levels in a Test Pyramid