Uniswap

Uniswap is based on an idea that the Ethereum founder Vitalik Buterin had in 2016.

Uniswap was created on November 2, 2018 by Hayden Adams, a former mechanical engineer at Siemens (he received $100,000 from the Ethereum Foundation to build the DEX).

Until Uniswap became a thing most exchanges handled their trades with an order-book that matched buy and sell orders, but they had a problem with illiquid assets because there was no incentive for market makers to provide their liquidity. Uniswap solves this by allowing everyone to become a market maker by adding their tokens in a pool and it rewards them with the collected trading fees.

Since Uniswaps success there has been a big revolution in the entire DeFi market. That is partly because dApps and developers of new projects can utilize a DEX to launch a new token or to let their application make trades while staying completely decentralized. A lending protocol for example can use a DEX to sell the provided collateral of a failed DeFi loan to cover the outstanding debt. Applications can also have a buy back and burn mechanism where a part of their fees is being used to buy their governance token back from a DEX to destroy them. A decentralized exchange is a necessary infrastructure for a DeFi ecosystem.

UNI is supported by every bigger exchange like Binance for example. Of course Uniswap itself offers it too. A Ethereum wallet like MetaMask can store the token and interact with the Uniswap app.