  In a world with an ever increasing urbanization, governance is investigating
innovative solutions to sustain the society evolution. Internet-of-Things
promises huge benefits for cities and the proliferation of smart city
deployments demonstrates the common acceptance of IoT as basis for many
solutions. The city pilots developments occurred in parallel and with different
designs thus creating fragmentation of IoT. The European project SynchroniCity
aims to synchronize 8 smart cities to establish a shared environment fostering
a self-sustained business growth. In this article we present the collaborative
methodology and shared efforts spent towards the creation of a common ecosystem
for the development of smart city services. Our design evolves around the
concept of "atomic services" that implements a single functional block to be
composed for full-fledged smart city services. This creates opportunities for
diverse stakeholders to participate to a global smart cities market. The
methodology and outcome of our efforts will be followed by 10 new cities
globally, thus expanding the market range for IoT stakeholders
