I don't think you can call them an airline. Seems to be more like a marketing umbrella for virtual airlines from various European countries that are willing to sell tickets under a common branding, to do joint marketing / distribution and jointly buy flight services from ACMI operators (initially from Denim Airways and later on from JOIN once it has got its own AOC). As far as I understand it, there are a couple of virtual airlines from Germany, the Netherlands, France, Belgium and the UK on board, but only one of them - German "Jetisfaction" - has already provided short-lived scheduled services from FMO to ZRH and POZ.
I am surprised that Executive Airlines is mentioned as a "JOIN" airline. Why would a reasonably successful biz jet operator be bothered to enter regional scheduled services?