postmanlabs
readme file does not explain what this service does
It is not clear what the service presented by this repo does.
The readme file lacks the explanation, and the links it points to do not explain either. The summary of it being a "HTTP Request & Response Service" does not convey much really.
dummy me wonders the same having being informed about this nice project. From the first view seems to provide example responses for various typical requests/scenarios. But that can't be just that, right? (will read to discover more)
The best conclusion I came to is that it is a web server that offers facilities to test Client-Side REST API calls.
i.e. you're writing a client-side code and want to test the behavior with a certain server response, so you use one of the URLs supported by this http.bin