Gelato is a protocol to automate smart contract executions on Ethereum. Even though smart contracts are sometimes described as "executing logic autonomously", their execution is actually far from automatic.
Actually, smart contracts are quite lazy. They always require an outside impulse (a transaction) to execute certain logic. For example, you cannot schedule a smart contract to send some Ether from your address to a friend in two weeks without actually sending the transaction yourself at that time. This makes building applications which require certain transactions to be scheduled and executed automatically at some future point in time quite hard to build. It usually boils down to developers having to run centralized scripts which execute the transaction on behalf of their users, making them the central point of failure in the whole process
This is exactly what Gelato aims to solve. Rather than you as a developer having to run your own, centralized bot which executes these transactions on behalf of your users, you can outsource that overhead to the Gelato Executor Network. This network consists of several bots running all the time, listening to new tasks that developers and their users can assign them. If one of these tasks becomes executable, then the network of bots will execute the transaction on behalf of your users. This means that you will no longer be the central point of failure and responsible for when your bot goes down while enjoying all the tooling and pre-made automation use cases the gelato community has already created.
Interesting example use case include:
Automatically minting Chi Gas tokens when gas prices are low (repo)
Automatic trading strategies, e.g. buy 100 USDC worth of ETH every day (repo)
One-time conditional trades on DEXs, e.g. placing a stop-loss order on Uniswap
Automatic Liquidity Withdrawals on Uniswap or prediction markets like Omen.eth (repo)