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.

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

Design, debug, and test APIs locally or in the cloud

Hoppscotch is an open-source API development ecosystem that helps you create and test your API requests saving precious time in development.

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.

Selenium automates browsers. That's it! What you do with that power is entirely up to you.