I made Smocker[1]. It's a mock server we use extensively with my coworkers because we develop Go HTTP "micro" services and most of the tests we write are integration/component tests. We needed a way to mock the external services to test our service in an isolated way. Before that we used http-mock-server but it came short in a lot of ways: JSON config (very bad when you need to configure it to return JSON payloads), bad performances (our tests made it crash routinely), big memory and space footprint (a bit annoying for our CI and for our test machines). So we made Smocker to fix these issues and add more useful features. It does less than http-mock-server but is more focused IMO.

[1]: https://smocker.dev