Green wallet has a unique Multi-Signature model using dual private keys – one held by the user, and one by their servers.
This allows a higher security mobile Bitcoin wallet system that can enforce Two-Factor Authentication to protect your funds, while time-lock smart contracts guarantee that users always retain full control of their coins.
No documents, personal information, or KYC required. All that is needed is a single email address. For even further privacy user can choose to not use an email and exclude some functionality of Blockstream Green Wallet.
Resources with more information.