More broadly, I would say public P2P stuff - at least in its current forms. I'm not sure it can survive some of the generational shifts that have been occurring in society, since it relies so heavily on community and sharing and demands general technological literacy (not just touchscreen/smartphone/app literacy). Those that do actually have the literacy seem increasingly interested in the instant gratification direct download or torrent streaming stuff, to the detriment of traditional methods of P2P file sharing.