[wehadfun]

Is there any hardware that uses MQTT?

[playing_colours]

There is. For example, we use it for our hardware product: https://www.relayr.io/products-services/wunderbar/

[sborsje]

Karma does: https://blog.yourkarma.com/how-we-use-mqtt-at-karma

[baldeagle]

My now somewhat defunt ninjasphere uses it. I've also heard it is popular with openHab or other IoT devices.