Bruno is a Fast and Git-Friendly Opensource API client, aimed at revolutionizing the status quo represented by Postman, Insomnia and similar tools out there.

Professional software tool for HTTP testing and debugging

Browser and Mobile Automation Test Framework for Node.js

Unifying API testing, API Performance testing, API Mocks and UI testing.

Requestly is an open-source tool that simplifies API development, testing, mocking, and integration for developers and QAs.

Burp or Burp Suite is a set of tools used for penetration testing of web applications. It is developed by a company named Portswigger who make freely available a Web Security Academy which has a range of lessons on penetration testing.