In the uprising of decentralised finance, there have been an influx of automatic market makers (AMM) appearing in the scenes. They have stemmed from the most basic use case of a decentralised exchange(DEX) with trading of 2 commodities that happen peer-to-peer via a liquidity pool.
Uniswap has been one of the first main competitors of AMM initially paving the way for the coming generations of AMM, and the code was contributed to the open source community who have quickly picked up the project, forking it and making improvements on it alongside the growth of the original Uniswap which is now moving onto version 3 of its DEX. Uniswap was originally built for the Ethereum VM (EVM) and was deployed to the Ethereum(ETH) network. Users who stake liquidity into the liquidity pair pools gain a portion of the DEX transaction fees.
Another variant of Uniswap is Sushiswap who's team sought to extend the AMM features provided, allowing users to easily do yield farming and this provides a good incentive for users to provide liquidity for the growth of liquidity pools used by the DEX. This yield farming rewards users for having staked liquidity.
Pancakeswap is yet another fork of Uniswap and also sought to extend the AMM features provided. Most the biggest incentive to migrate to Pancakeswap was to reduce fees and they achieved this by deploying their smart contracts to the Binance Smart Chain(BSC). The biggest difference at the time of deployment is that the ETH blockchain had not yet moved to a Proof Of Stake(PoS) consensus mechanism, hence ETH transactions were still expensive at the time. BSC already uses PoS consensus mechanism and the savings in transaction costs are huge, which has been one of the biggest problems for many users of DEX.
Pancake swap also provide liquidity farming, and they continue to extend their feature set of DeFi, today offering a Lottery and their latest feature being a binary options trading feature called "Predictions".
There have been further improvements to later generations of AMM which now tend to make a fork of Pancakeswap or sibling. One such AMM is known as PantherSwap and they have included tokenomics most recognised by the SafeMoon tokenomics where they automate liquidity acquisition for their pools. The tokenomics work such that a tax is made on each transfer of the underlying token, PANTHER. This tax is then split up and provided to the PANTHER holders and also liquidity pools.
Running even further away from transaction fees, PolyLion have forked Pancakeswap in a similar manner to PantherSwap using SafeMoon tokenomics. PolyLion have however deployed their contracts to the Polygon blockchain - formerly known as Matic-, and this chain has negative transaction fees, hence you are paid MATIC to interact with these contracts.
Today there are 100s of AMM in existence generally forked from PancakeSwap as the current AMM/DEX leader. Each AMM is trying to reduce the costs and slippage of DEX transactions with their own unique features.