3 minute explanation of Ethereum by inventor Vitalik Buterin.
Ethereum is a platform that makes it possible for any developer to write and distribute next-generation decentralized applications.
Borrowing the concept of distributed consensus and cryptographic proof that makes cryptocurrencies such as Bitcoin so effective in trustless payments, Ethereum extends the use of these technologies to trustless agreements. This allows developers to easily build innovative new products on a censorship and collusion-resistant foundation.
Main site: https://www.ethereum.org