Ethereum, initially described in a white paper by cryptocurrency researcher and programmer Vitalik Buterin in 2013, is an open-source, public, blockchain-based distributed computing platform featuring smart contract (scripting) functionality. It provides the Ethereum Virtual Machine (EVM), a decentralized Turing-complete virtual machine which can execute scripts using an international network of public nodes. Ethereum also provides a value token called “ether”, which can be transferred between participants and is used to compensate participant nodes for computations performed. Gas, an internal transaction pricing mechanism, is used to prevent spam on the network and allocate resources proportionally to the incentive offered by the request.
Ethereum development was funded by an online crowdsale during July–August 2014. The system went live on 30 July 2015. Since the initial version, the Ethereum network has accomplished several so-called hard forks, important changes because they are backwards-incompatible. For instance, a hard fork that occurred on July 20, 2016, resulted in two separate blockchains: Ethereum and Ethereum Classic. Ethereum Classic is a separate blockchain that came into existence as a result of the DAO hard-fork, consolidating members of the Ethereum community who rejected this fork on philosophical grounds.