A non-functional evaluation of Open Source projects should be based on a methodology with a set of questions; answers to questions should be based as much as possible on measurable facts.
Roberto Galoppini, the author of SOS Open Source http://sosopensource.com has developed such a methodology refining existing ones. SOS Open Source's author has then developed a tool supporting the assessor in the application of such methodology; the output of SOS Open Source tool produces reportx showing graphically how different projects meet SOS Open Source evaluation criteria. Roberto Galoppini has granted Bitergia and the PROSE project a perpetual, non-exclusive, non-transferable, worldwide, limited license to access and use the source code and the methodology in order to create enhanced versions of the tool and the methodology preserving the original licenses (SOS Open Source AGLP for the source code, and CC-BY-NC-SA http://creativecommons.org/licenses/by-nc-sa/2.0/ for the methodology. Within the PROSE project the methodology has been refined and the software tool fully rewritten preserving the idea of the original code.