A quick project from a few months back that never quite made it to the blog. We were keen to see how much data was flowing through the MQTT broker.
This quick javascript page displays a live feed with running totals of sensors seen since the page opened. Press the space bar to pause the stream.
https://www.iot.io/projects/east-iot-stream/
Update (20th Nov 24): Steve also created this one https://mqtt-live.cetools.org