Here are some other successful (and not so successful) internet currencies

DigiCash started it off but went bust
Founded in 1990 by David Chaum, DigiCash was one of the first electronic currencies but was went bust almost a decade later when Mark Twain bank – the only bank that supported the business – decided to withdraw its backing.

Mint Chip focuses on small transactions
MintChip is The Royal Canadian Mint’s attempt to compete with anonymous transaction currencies like Bitcoin. Launched this year, it is designed to cope with small transactions.

Zero cost payments with Zen
Ven is a global digital currency used by Hub Culture members, who share and exchange knowledge related to their businesses, to buy, share, sell and trade. It’s main use is to send and receive payments online for zero cost.

Share virtual content with Linden Dollar
The Linden Dollar is the currency of Second Life, an online virtual community and social network. Second Life is a place where people can buy and sell virtual content that they have created.