Product innovation assessment in software sector is a timely topic. Nevertheless, research on that subject is particularly scant. As a result there is a lack of criteria to measure software innovativeness. In a context of theoretical and practical controversy in the open source field, this article assesses open source software innovativeness. Based on almost 500 cases studies and with the collaboration of 125 experts from industry, services and research fields, it suggests an innovation typology supported by the notion of functional added value. It provides also an innovation modelling framework that combines main evaluation methodologies. By showing the shortcomings of widely used innovation metrics, this research supports a new approach of innovativeness assessment specialized in each sector.