The IA92 supportpac includes a light-weight Java GUI for using MQTT.
There is general agreement we should have a replacement utility as a part of paho. IN fact, there is no reason we couldn't have a utility in each of the languages we provide client APIs for.
Before we each go off and write our own gui in our favourite language, we should but some work in up front to design, in a language agnostic way, what the utility should look like and what features it should provide.
As IA92 already exists, we should treat that as the initial straw-man for discussion.