Ganache is a local blockchain setup for coding, testing and developing Ethereum smart contracts.
Ganache offers you several accounts which who you can interact with your smart contract. The accounts have a certain amount of Ether and an address. It helps you to inspect the state while firing transactions and calling functions of your smart contract.
There is no local Ethereum client necessary which makes the setup faster and more stable.
The website features also some tutorials that help you to set up Ganache and use it in your production.
Ganache is part of truffle.