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.

Swagger UI allows anyone — be it your development team or your end consumers — to visualize and interact with the API’s resources without having any of the implementation logic in place

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

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

Website and mobile testing at every stage of 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.