Force.com Streaming Api Demo
This is an open source OSX 10.7 demo app that uses the Force.com Streaming API, once you've logged in, you can create new PushTopics, subscribe to any number of them, and see the events as they arrive. You can click on an event in the event list to see all the details.
Downloadsv1 : July 9, 2011, (90kb)
Source code is available on Github