It's been a while since there has been an update here, so in lieu of one here are some interesting links I've come across recently. Add a comment to the post if you've done something cool not mentioned here! Work progresses on mosquitto 1.2.

Initial release of an MQTT-S gateway, written in ruby:

And some MQTT-S tools:

A Pinoccio/MQTT/sensor powered Theramin:

Voice controlled MQTT LED:

An MQTT notification plugin for Jenkins/Hudson: