This model (Figure 1) supports us to separate and examine three main issues, which are addressed in different subsections. In 2.1, we look at the different kinds of development tools that are supported. This helps to characterize the type of technology each platform provides for developers (e.g., software development kit). More precisely, we determine if the technology provided has an open access or not (i.e., opensource versus proprietary sources). In 2.2, we describe the different types of portals for each platforms. We characterize portals that act as intermediaries between developers and consumers. We differentiate between