We started writing zerorpc in 2010. We did test msgpack-rpc at the time, but it was barely a proof-of-concept.
A few key differences: zerorpc supports zeromq (including pub-sub and push-pull topologies), streaming responses, and has a bunch a of great instrumentation built on top of it.
Somewhat of a side-note, but interestingly enough, MessagePack's author cited ZeroRPC as a good example of MessagePack's use case: https://gist.github.com/2908191
http://msgpack.wordpress.com/category/messagepack-rpc/ http://wiki.msgpack.org/display/MSGPACK/Design+of+RPC
How zeroRPC differs from that in performance, perspective and status? Did you know of msgpack-rpc when started zeroRPC?