This gem wraps the ZeroMQ networking library using the ruby FFI (foreign function interface). It's a pure ruby wrapper so this gem can be loaded and run by any ruby runtime that supports FFI. That's all of them - MRI 1.9.x, Rubinius and JRuby.
Gemfile gem 'ffi-rzmq', '~> 0.9.6'
install gem install ffi-rzmq -v 0.9.6