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.

HyperTest is a no-code test automation tool that regresses all your APIs by auto-generating integration tests using your network traffic, also giving a way to reproduce these failures inside actual user-journeys.

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

Bugs. Happen. Debugging and Troubleshooting Reimagined

Fully integrated API and web service testing capabilities that automate end-to-end functional API testing.

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.