Uniswap is a decentralized exchange that facilitates automated transactions between Ethereum-based tokens. It is designed to be an open-source platform with an automated market maker (AMM) model. Instead of using an order book, token trades are facilitated directly between users through a liquidity pool and prices orders with an algorithm that relies on the equation x*y=k to create a price spectrum for token pairs available in the liquidity pools provided by other users. Uniswap tokens are used as a governance token and as an incentive for users to fund the liquidity pools. Since the platform is decentralized, all the trading fees collected are distributed among the liquidity providers; according to the share that they provide in the liquidity pools.
Uniswap is one of the largest decentralized exchanges (DEX) and one the largest cryptocurrency exchanges overall by daily trading volume. The platform was originally created by Hayden Adams, a former mechanical engineer at Siemens. It is backed by some influential venture capital funds, including: Andreessen Horowitz, Paradigm Venture Capital, and Union Square Ventures.

SushiSwap is a decentralized exchange protocol that emerged as a fork of UniSwap. The main difference being the SUSHI token which acts as a governance token and entitles holders to a percentage of the trading fees charged on the network. Both UniSwap and SushiSwap, use an automated market making (AMM) model, where liquidity providers add funds to liquidity pools. Unlike centralized, order book exchanges, token pairs are priced according to an equation in which multiplying the prices of the 2 tokens will always equal a constant.

Newdex is the first EOS based decentralized exchange. It's built on the EOS main chain and uses an off-chain matching mechanism to pair buyers and sellers. Newdex was hacked in September 2018, and lost around $58,000 worth of cryptocurrencies. Trading fees are 0.1%.