Chainlink (LINK)

A smart contract cannot fetch an exchange rate or a match result on its own: it sees only what is written on chain. Chainlink closes that gap — a network of independent operators collects data from outside sources, reconciles the readings against each other and publishes an agreed value on chain.

A price feed is assembled from many nodes and many sources, and it refreshes not on a clock but whenever the price drifts past a set threshold or a heartbeat interval elapses. Such feeds became infrastructure for lending protocols and derivatives: collateral is valued and liquidations are triggered off them, so the oracle's reliability directly determines the solvency of the applications reading it. Beyond prices the network relays messages between blockchains, attests to issuers' reserves and supplies verifiable randomness.

The LINK token pays operators for their work and serves as the collateral they stand to lose for dishonest reporting.

An oracle is a single point of failure for everything downstream of it: a wrong published price triggers liquidations the market never justified.