As early as tomorrow (September 18th), Ethereum could roll out the first iteration of the Metropolis hard-fork called the Byzantine hard-fork.
Ethereum has been in step two of its launch process called Homestead and Metropolis is a major step in the Ethereum platform. When the Ethereum network reaches block number 1,700,000, the hard fork will go live on Ethereum’s Ropsten Testnet.
You can view the testnet on Etherscan. At press time it the latest block number is 1,694,579.
Metropolis is when The Ethereum Foundation will release a full-featured user interface for non-technical users of Ethereum. Mist will launch with a dApp store and several projects will be featured, to show the full power of the network. With Metropolis, Ethereum intends to support large decentralized applications with millions of users.