This is test.mosquitto.org. It hosts a publicly available Mosquitto MQTT server/broker. MQTT is a very lightweight protocol that uses a publish/subscribe model. This makes it suitable for "machine to machine" messaging such as with low power sensors or mobile devices.
For more information on MQTT, see http://mqtt.org/ or the Mosquitto MQTT man page.
If you've written a client that is now unable to connect, please get in touch (I am @ralight on twitter). Your app is not well behaved but would be easy to fix!
The server is available at test.mosquitto.org on tcp port 1883, the standard MQTT port. You are free to use it for any application, but please do not abuse or rely upon it for anything of importance. You should also build your client to cope with the broker restarting.
If you have the mosquitto clients installed on Linux/Mac, try:
Or on Windows:
I reserve the right to remove the service at any point, but am only likely to do so if it is not used at all or is exceeding my bandwidth limits.
A web based push demo is available. This is the demo as provided by tokudu.com, but running locally.