How many stable and active libre software projects?

Carlo Daffara has been estimating, in the context of the FLOSSMetrics project, the number of active and stable libre (free, open source) software projects. He estimates that a lower bound for this number is about 18,000 (considering only those in the global libre software community, some more regional or local projects do exist). A good share of them will be studied in detail by the FLOSSMetrics projects...