Currently there are dozens of different blockchains, separate from Ethereum, all running their own transactions and developing their own products and applications.
Ethereum was the first blockchain to allow applications to be built on it. It is by far the most popular blockchain for web3 development, covering the highest amount of transactions. Many users have their crypto on Ethereum-compatible wallets.
Aurora provides affordable Ethereum compatibility for NEAR. This means applications written with Aurora are compatible on both NEAR and Ethereum.
Aurora also acts like a bridge between Ethereum, NEAR, and Aurora, allowing users to send their crypto and assets from NEAR to Ethereum and vice-versa. This is called NEAR's Rainbow Bridge. You can access the bridge through this link.