Ethereum

Ethereum started when someone controversially decided to shove a virtual machine state inside of each block.

Programs (or "Smart Contracts") are deployed to specific addresses. Each one has some binary interface for read/write functions with varying levels of access control.

These programs are typically used to perform various bookkeeping duties for ETH balances and various tokens.

Some of the most interesting use cases are stablecoin protocols and decentralized (non-custodial) exchanges.