There is not currently a publicly accessible demonstration server. What kinds of actions were you wanting to try out? If you just need a source of streaming data, we could probably find one. If you need a server where you can create/modify streams of data then you would probably be better off with a server that you have exclusive access to so that other people aren't modifying streams at the same time as you are.
Tim, how to define those streams in GeoEvent Processor? I've tried to use Subscribe to an external Web Socket for JSON connector with different combinations of url (using ws:// and http://) but incoming data count is "0". Of course I'm able to see the stream using any internet browser.
It appears that we have an issue leveraging the out-of-the-box connectors for the 10.2.0 product to consume feeds available from the http://geoeventsample1.esri.com/demosite. We are currently looking for a work around.
We apologize for the inconvenience. I'll post to both this thread and the thread referenced above if we can find a work around which doesn't require a patch to the product.