Any good integration emulators available?

On my current project in my team uses own custom Spring application for integration emulation. It allows us to answer to SOAP/MQ/SMTP requests with different responses. This tools is useful for testing integrations (which we have a lot of). Unfourtanetly, it's not as extensible and convenient as we want it to be.

Are there any good ready applicatons implementing this functionality or should we stick to refactoring our current testing application? Google hasn't given me any aplications of that kind.

Thank you!