The Ethereum main testnet server Ropsten is a public test network that allows developers to test their applications before they launch them on the Ethereum main network. The Ropsten network is a replica of the Ethereum main network, but with reduced functionality. The Ropsten network is used to test new features and applications before they are deployed on the Ethereum main network. The Ropsten network is also used to test smart contracts and other applications.
The Ropsten network has its own currency, called Ether, which is used to pay for transaction fees and gas costs. The Ropsten network also has its own blockchain, which is separate from the Ethereum main blockchain.
The Network ID for the Ethereum main testnet server Ropsten is 3.