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

Hand-crafted lightweight Rest Client for testing APIs. Supports collections, environments, git collaboration and local storage.

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

Voiden is a developer-first API client with local storage, Git-integrated, all based on markdown + offline support.

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.