Bitcoin

Bitcoin is a virtual currency not supported by a central issuer, but by all users. It uses open-source software to send, receive and generate money. It is a form of cryptocurrency, relying on cryptography as well as peer-to-peer technology to work. Bitcoin is designed in such a way that you can send and receive money anonymously.

Bitcoin is probably the first usable implementation of cryptocurrency, which was first described in 1998 by Wei Dai on the cypherpunks mailing list.