Sharing data in peer-to-peer mode is possible between deployments sharing a mothership. A Mothership is an S3DB deployment where each deployment can register during configuration. See Register for more information.
A user in a deployment (D1U1) can share a certain S3DB Uid, for example a Project (Px) located in that certain deployment (D1) where user has permission with another User (D2U2) who has been created in another deployment (D2).
The user needs only to indicate the deployment of the remote user (D2) in the S3QL query, for example:
See also S3QLSyntax.