Bitcoin

Bitcoin is the first and original distributed currency. The actual Bitcoin idea specifies how to securely and irreversably distribute or transmit "value" over the Internet.

Bitcoin is a massive distributed ledger of transactions, that is held by every Bitcoin user. To send value, I announce that I am transfering some Bitcoins to another user. The announcement validated and spread by the network, each user checking first, that I had the Bitcoins to send, then confirming the transmission.