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

Test, scrape, generate, and automate without the pain and expense of hosting your own headless browsers.

Jest is a delightful JavaScript Testing Framework with a focus on simplicity.

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

Playwright enables reliable end-to-end testing for modern web apps.

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.