For Ethereum, Defi.(Decentralized finance). Basically crypto based financial services run on smart contracts as Decentralized Autonomous Organizations (DAOs). Services include lending and borrowing, decentralized exchange, insurance, stablecoins, derivatives, portfolio management and more.

MakerDao, Uniswap, Compound Finance, Yearn Finance, just to name a few. It's only just starting to take off, see more metrics here https://defipulse.com/

Another area taking off on Ethereum right now are "Non Fungible Tokens". Basically digital art trading on crypto.