Bitcoin is both a cryptocurrency and an electronic payment system.

Litecoin (LTC) is a peer-to-peer cryptocurrency and open source software project.

Groestlcoin is a multipurpose cryptocurrency that has instant & private transactions with minimal fees.

Nxt is an open source cryptocurrency and payment network.

Peercoin (PPCoin or PPC) is a peer-to-peer cryptocurrency utilizing both proof-of-stake and proof-of-work systems.