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.