Postman is an API platform for building and using APIs. Postman simplifies each step of the API lifecycle and streamlines collaboration so you can create better APIs—faster.

API Testing Platform that automatically generates unit test cases with dependency mocks from API calls

Design, debug, and test APIs locally or in the cloud

A modern, resource-friendly REST client for Windows 10

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.

Vigil is an open-source Status Page you can host on your infrastructure, used to monitor all your servers and apps, and visible to your users.