Below is a copy of the SDK that I received in April 2015. I successfully built and ran the AndroidMelonBasicSample application on my Motorola phone. It actually communicated with the Melon headband!
Melon was purchased by DAQRI in February 2015. They still maintain a Melon product page, but the Google+ Melon Headband – Android Users community (see update below) has been all but silent for over 6 months. That plus the website message “We’re back in the lab crafting new things” is a good indication that Melon development is no longer active.
Update (4/6/16): The community has shut down: