Currency is something of a misnomer. "Cryptocurrency" lacks the defining features of a currency, namely, the full faith and credit of an established government, and the accompanying legal mechanisms to ensure that it is honored as a medium of exchange. At the moment, I would describe Bitcoin and its cousins as elaborate private barter authentication mechanisms, which happen to have spawned an intensely speculative investment market that depends on legal currency for its existence. I wouldn't even say they're equities, because they have no intrinsic relationship to any tangible assets. They only have value among the self-selected participants in a virtual bazaar that offers a very narrow range of niche products for barter, and even then only after the bitcoins have been exchanged for actual currency, in most cases.