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

Uptime Kuma is an easy-to-use self-hosted monitoring tool.

The world’s first API testing platform that auto-generates unit test cases with dependency mocks from API calls. Using advanced AI, it simplifies test creation, debugging, and evolution, ensuring comprehensive coverage and boosting software quality.

Easy-to-use website monitoring and uptime monitoring service in one

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

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.