What are zeromq use cases?

IPython uses ZeroMQ for parallel computing features, the qt console and the notebook.

Let's say you want to have a bulletin board of some kind. You want to allow only some people to see it, by subscribing to the bulleting board.

This can be done using the publisher/subscriber model of ZeroMQ.

Now, let's say you need to send some asynchronous messages. That is, when a message is sent from system A and needs to get to system B, it is guaranteed to be delivered later, even if systems A and B cannot communicate at the moment when that message is sent. You can imagine a use case being SMS messages.

This can be done using asynchronous messaging model of ZeroMQ.

Basically, any JMS compliant solution like ZeroMQ will allow you to reliably broadcast or send a "message", whatever that message may be, to some other party with as little hassle as possible.

Please see the ZeroMQ blog -- they regularly post usage stories about different deployments, language bindings, etc.

Last time Rick Olson created a "clone" of Dropbox: https://gist.github.com/122849a52c5b33c5d890