Snapshot is a decentralized voting system. It provides flexibility on how voting power is calculated for a vote. Snapshot supports various voting types to cater to the needs of organizations. Creating proposals and voting on Snapshot is user-friendly and does not cost gas as the process is performed off-chain.
In short, Snapshot is an off-chain gasless multi-governance client with easy to verify and hard to contest results.
On Snapshot is:
Read more about snapshot here.
Sushi's snapshot space can be found here.