Bitcoin is a global form of digital currency. Unlike traditional currencies, which were frequently backed by gold and silver, bitcoin is based on distributed computing. While traditional currencies are printed by central banks, bitcoins are created or "mined" by distributed computer networks.
Bitcoin differs from traditional currencies is that it is decentralized, meaning that it is not controlled by any single institution. As a result, miners around the world create new units of the currency and confirm its transactions.
Ethereum, is a decentralised platform that runs smart contracts.
Ether is the digital currency used by Ethereum. Ether is the fuel or "gas" used to pay for transactions made on the Ethereum platform. Ether gives participants a reason to contribute resources used by the platform, thereby ensuring a robust network. Further, it provides developers with incentive to write efficient code, as inefficient software programs are more expensive.
Litecoin is an open-source, decentralized digital currency that was created in 2011 using code from a Bitcoin client. Because of the close relationship between the two, many have described Litecoin as being the Silver to Bitcoin's gold.