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

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.

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

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.