zmqc is a small but powerful command-line interface to ØMQ. It allows you to create a socket of a given type, bind or connect it to multiple addresses, set options on it, and receive or send messages over it using standard I/O, in the shell or in scripts. It’s useful for debugging and experimenting with most possible network topologies.
As an aside, text rendered using light fonts in grey is nigh-unreadable, especially against a white background. Don’t do that to your readers, it’s not nice.