How does a monome work?

monome.org sells monome devices. I am not affiliated with monome. I did not make the hardware. I use monome controllers with software I create to test ideas I have for real time music software interaction. My public work can be found at github.com/stretta
I made this video for my viewers to answer the common question: what is that thing and how does it work? I will make another video to answer the question: why I use the monome.