What is the main use of Ethereum?

Could you please elaborate on the primary utility of Ethereum? I'm interested in understanding how it differs from other cryptocurrencies and what specific applications it has within the blockchain ecosystem. Could you provide some examples of how Ethereum is being used in practice, and perhaps explain the significance of its smart contract functionality? I'm also curious to know about any potential challenges or limitations associated with its usage. Thank you for your assistance in clarifying these points.