Listed on the ServiceStack website it shows that ServiceStack can run on Mono with either:
evhttp-sharp - http server with host for NancyFx
https://github.com/kekekeks/evhttp-sharp
Very fast, almost 4 time faster than nancy-libevent2.
http://www.techempower.com/benchmarks/#section=data-r8&hw=i7&test=json&s=2&l=2
There are test results for different configurations:
JSON responses per second: