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

YATTIE exists to help make tester's lives easier. Ideally, it should remove friction from the exploratory testing process - everywhere from gathering evidence to submitting reports.

Robot Framework is a generic open source automation framework. It can be used for test automation and robotic process automation (RPA).

Browser and Mobile Automation Test Framework for Node.js

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.

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.