I'm Kjell-Åke, the developer, the support guy and founder of WebMaestro. As a consultant I was developing microservices and Biztalk integrations for customers. I had to perform HTTP API testing of what I had developed, but I couldn't find a tool that was good enough to use for this.
So I developed my own HTTP API testing tool that allowed me to both send HTTP requests and mock HTTP API:s in the same app. No other tool could do this in a simple way without having to install a separate web server for mocking API:s.
If you would like to contact me, send me a DM on Twitter @kjellegafvelin.