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There are enough open-source clients (like Furi).

The short-lived Open Source arm of Nullsoft, Gnullsoft, created GNUtella. When the earlier clients were released Gnutella 0.X they were released for developer preview. Their original plan was to keep it closed source while they whacked out all the bugs and open it when it reached the 1.0 stage. Needless to say, it never made it that far, the project was killed by AOL. Slowly, the developer versions made its way across the Internet and people started figuring out how the protocol worked. After a while the protocol was understood enough that the "clones" started coming out. Most of these were for fun and crap, not really to impressive. After time the protocol became more and more understood more sophisticated clients arrived fixing many bugs in the original Gnutella 0.X clients. The original clients became obsolete and Gnutella went form a program and a protocol to just the protocol.