Also not relational, but Meteor (MongoDB) with GroundDB for the client provides optimistic UI, offline persistence, and sync on reconnect. Unlike Couch / Puch,

Also not relational, but Meteor (MongoDB) with GroundDB for the client provides optimistic UI, offline persistence, and sync on reconnect. Unlike Couch / Puch, you can easily share a DB between users with authentication / authorization. Synced content can be controlled with subscriptions.