Maintainability is a key factor for the evolution of an open source system due to the highly distributed development teams that contribute to many projects. In the literature there are a number of different approaches that has been developed to evaluate the maintainability of a product but almost each method has been developed in an independent way without leveraging on the existing work and with almost no independent evaluation of the performance of the models. In most of the cases, the models are only validated through a limited set of projects only by the people that propose the specific approach. This paper is a first step towards a different direction focusing on the independent application of the existing models to popular open source projects.