Etherscan

Basics

• Allows you to explore and search the Ethereum blockchain for transactions, addresses, tokens, prices and other activities taking place on Ethereum.
• Has become the de-facto place to go to for Eth tx details. So much so, Anthony Sassano questioned its dangers due to it being a centralized website.

Tech

• Uses technology built by Parity.

Competitors

• Ethplorer, Bitquery, and other block explorers.

Team

• The team behind Etherscan also made a block explorer for Grin.