Mountebank

Mountebank is an open source tool which can execute multi-protocol tests. The codebase is Node JS. It is easy to create stubs and mocks.

Features:
Mountebank tool aims to be fully cross-platform, with native language bindings
It is non-modal and multi-protocol solution. It can test SMTP, HTTP, TCP, and HTTPS
This tool provides service virtualization service free of cost without any platform constraints
Frequently updated, mature, and stable tool.

More Information and Official Website:
Download link: http://www.mbtest.org/